The Crazyist Metaphysics of Mind


Eric Schwitzgebel

Department of Philosophy

University of California

Riverside, CA  92521


eschwitz at domain:


February 28, 2012


The Crazyist Metaphysics of Mind




Crazyism about X is the view that something that it would be crazy to believe must be among the core truths about X.  In this essay, I argue that crazyism is true of the metaphysics of mind.  A position is “crazy” in the intended sense if it is contrary to common sense and we are not epistemically compelled to believe it.  Views crazy in the intended sense include that there is no mind-independent material world, that the United States has a stream of conscious experience distinct from the experiences of the individuals composing it, that chimps or the intelligent-seeming aliens of science fiction fantasy entirely lack conscious experience, that mental events are causally inefficacious.  This is by no means a complete list.  Well developed metaphysical theories will inevitably violate common sense, I argue, because common sense is incoherent in matters of metaphysics.  No coherent and detailed view could respect it all.  Common sense is thus impaired as a ground of choice.  Nor can scientific evidence or abstract theoretical virtue compellingly favor any one moderately specific metaphysical approach over all competitors.  Something bizarre must be true about the mind, but which bizarre propositions are the true ones, we are in no good position to know.



The Crazyist Metaphysics of Mind


Mysterians about the mind – Colin McGinn (1989, 2004), Noam Chomsky (2009) – say that we will probably never know how conscious experience arises from the brain.  But here’s one thing we do generally know, according to them: Whatever the process involved, it’s “natural”.  No hand of God, no immaterial souls required.  But I wonder, if we know as little as they say, why rule out deities and immaterial souls?  If the soul seems a strange and unnatural thing, alien to our science, well, our science is an impoverished tool for penetrating the mysteries of the universe, they say.  A turtle might find strange and unnatural a container ship and might find almost ethereal a schedule of amortization.  If we are but somewhat upgraded turtles, our sense of unnaturalness is no rigorous index of reality.

In this essay I propose a more deeply skeptical mysterianism about the mind than that of McGinn and Chomsky.  On my view, it is probably the case that something it would be crazy to believe – something bizarre and undeserving of credence – is among the core metaphysical truths about the mind.  And immaterial souls aren’t ruled out.




Bizarre views are a hazard of metaphysics.  The metaphysician starts, seemingly, with some highly plausible initial commitments or commonsense intuitions – that there is a prime number between 2 and 5, that I could have had eggs for breakfast, that squeezing the clay statue would destroy the statue but not the lump of clay.  She thinks long and hard about what, exactly, these claims imply.  In the end, she finds herself positing a realm of abstract Platonic entities, or the real existence of an infinite number of possible worlds, or a huge population of spatiotemporally coincident things on her mantelpiece.[1]  I believe that there is not a single broad-ranging exploration of the fundamental issues of metaphysics that doesn’t, by the end, entangle its author in seeming absurdities (sometimes advertised as “surprising conclusions”).  Rejection of these absurdities then becomes the commonsense starting point of a new round of metaphysics, by other philosophers, which in turn generates a complementary bestiary of metaphysical strangeness.  Thus are philosophers happily employed.

I see three possible explanations of why philosophical metaphysics is never thoroughly commonsensical:

First possible explanation.  A thoroughly commonsensical metaphysics wouldn’t sell.  It would be too boring, perhaps.  Maybe a famous philosopher can’t say only obvious things.  Or maybe it would lack a kind of elegant serviceability or theoretical panache.  Or maybe it would conflict too sharply with what we think we know from science.  The problem with this explanation is that there should be at least a small market for a thoroughly commonsensical philosophy, even if that philosophy is gauche, staid, and scientifically stale.  Common sense might not be quite as fun as Nietzsche’s eternal recurrence (1883-1888/1967) or Leibniz’s windowless monads (1714/1989); it might not be as elegantly useful as Lewis’s possible worlds (1986) or as scientifically current as __________ [insert ever-changing example]; but a commonsensical metaphysics ought to be attractive to at least a certain portion of philosophers.  At least it ought to command attention as a foil.  It oughtn’t be so downmarket as to be entirely invisible.

Second possible explanation.  Metaphysics is very difficult.  A thoroughly commonsensical metaphysics is out there to be discovered; we simply haven’t found it yet.  If all goes well, someday someone will piece it all together, top to bottom, with no serious violence to common sense anywhere in the system.  I fear this is wishful thinking against the evidence.  In the next several sections I will discuss the case of the metaphysics of mind in particular.

Third possible explanation.  Common sense is incoherent in matters of metaphysics.  Contradictions thus inevitably flow from it, and no coherent metaphysical system can respect it all.  Although ordinary common sense serves us fairly well in practical maneuvers through the social and physical world, common sense has proven an unreliable guide in cosmology and probability theory and microphysics and neuroscience and macroeconomics and evolutionary biology and structural engineering and medicine and topology.  If, as it seems to, metaphysics more closely resembles these endeavors than it resembles reaching practical judgments, we might excusably doubt the dependability of common sense as a guide to metaphysics.[2]  Undependability doesn’t imply incoherence, of course.  But it seems a natural next step in this case, and it would tidily explain the historical fact at hand.

On the first explanation, we could easily enough invent a thoroughly commonsensical metaphysical system if we wanted one, but we don’t want one.  On the second explanation, we do want one, or enough of us do, but we haven’t yet managed to pull it off.  On the third explanation, we can’t have one.  I hope you’ll agree with me that the third has at least some prima facie merit.  In sections iii-viii I will further explore the role of common sense in the metaphysics of mind.

Common sense might be culturally variable.  So whose common sense do I take to be at issue in this argument?  I suspect it doesn’t matter.  All metaphysical systems in the philosophical canon, I’m inclined to think, conflict both with the common sense of their milieu and with current Western common sense.  Much of the human worldview is stable over time, especially in Western societies since the early modern period.  Eternal recurrence, windowless monads, and the real existence of an infinitude of possible worlds were never part of any society’s common sense.

Some readers will disagree about the existence of the phenomenon I aim to explain; they will think that there is a thoroughly commonsensical metaphysics on the market.  To some extent, I’m simply taking as a premise that there is none, and I’m inviting you to agree based on your own reading of historical and contemporary metaphysics.  Maybe the premise will appeal better, though, if I highlight its intended scope.  It concerns only broad-ranging explorations of fundamental metaphysical issues, especially the issues where seeming absurdities congregate: mind and body, causation, identity, the catalogue of entities that really exist.  Some skating treatments and some deep treatments of narrow issues might dodge the charge.

Who might count as a thoroughly commonsensical metaphysician?  Aristotle, I’ve sometimes heard.  Or Scottish “common sense” philosopher Thomas Reid.  Or G.E. Moore, famous for his “Defence of Common Sense” (1925).  Or “ordinary language” philosopher P.F. Strawson.  But Aristotle didn’t envision himself as developing a commonsensical view: In the introduction to the Metaphysics Aristotle says that the conclusions of sophisticated inquiries such as his own will often seem “wonderful” to the untutored and contrary to their initial opinions (4th c. BCE/1928, 983a; θαυμαστόν: wonderful in the sense of tending to cause wonder, or amazing); and Aristotle generally conceives his project as in part to distinguish the true from the false in common opinion.  Moore, though fierce in wielding common sense against his foes, seems unable to preserve all commonsense commitments when he develops his positive views in detail, for example in his waffling about “sense data” (1922, 1953, 1957).  Strawson struggles similarly, especially in his 1985 book, where he can find no satisfactory commonsense account of mental causation.  Reid I will discuss briefly in section vi.

The argument of this section is an empirical explanatory or “abductive” argument.  The empirical fact to be explained is that all existing metaphysical systems are bizarre in some of their major features.  An attractive possible explanation of this fact, I submit, is that common sense is incoherent on matters metaphysical, so that no self-consistent and detailed metaphysical system can satisfy all commonsense constraints.




Let’s call a position bizarre if it’s contrary to common sense.  And let’s say that a position is contrary to common sense just in case a majority of people without specialized training on the issue confidently, but perhaps implicitly, believe it to be false.  Claims about common sense are empirically testable, but not always straightforwardly so.  It might, for example, sometimes be difficult to clarify the target claim – e.g., that there is a “Platonic realm” – without either mangling the target view or altering the respondent’s attitude toward it; and what is implicitly believed may be only tenuously connected to explicit questionnaire responses.  The best first-pass measure of commonsensicality might be specialists’ own impressions about the degree of conflict between positions in their field and non-specialists’ attitudes, as remembered from their training and reinforced in their teaching, with contentious cases to be referred for more systematic empirical study.

To call a position bizarre is not necessarily to repudiate it.  General relativity is bizarre.  Various bizarre things are true about the infinite.  It’s bizarre yet true that a black and white disk will look colored if spun at the right speed.  Common sense errs, and we can be justified in thinking so.  However, we are not ordinarily justified in accepting bizarre views without compelling evidence.  In the matters it traverses, common sense serves as an epistemic starting point that we reject only with sufficient warrant.  To accept a bizarre view on thin grounds – for example, to think that the world was created five minutes ago, or that you are constantly cycling through different immaterial souls, or that the universe was sneezed out by the Great Green Arkleseizure (assuming you have no special warrant for these views) – seems crazy.  I stipulate, then, the following technical definition of a crazy position: A position is crazy if it’s bizarre and we are not epistemically compelled to believe it.

One needn’t, of course, be clinically insane to accept crazy views, and not all crazy views are as crazy as the three just mentioned.  Many philosophers and some scientists embrace positions contrary to common sense and for which the evidence is less than compelling.  In fact, to convert a position from crazy to merely bizarre might be the highest form of academic success.  Einstein, Darwin, and Copernicus (or maybe Kepler) all managed the conversion – and in the case at least of Copernicus common sense eventually relented.  Intellectual risk-takers nurture the crazy and see what marvels bloom.  The culture of contemporary Anglophone academia, perhaps especially philosophy, overproduces craziness like a plant produces seeds.

Crazyism about a topic, then, is the view that something crazy must be among the core truths about that topic.  Crazyism can be justified when we have good reason to believe that one among several bizarre views must be true but where the balance of evidence leaves no individual view decisively supported over all the others.  We might find ourselves rationally compelled to believe that either T1, T2, T3, or T4 must be true, where each of the T’s is crazy.

Crazyism might be justified in interpreting quantum mechanics.  The “many worlds” and “many minds” interpretations, for example, sharply conflict, it seems, with ordinary common sense.[3]  And it also seems that the balance of evidence does not compellingly favor either of these views over all competitors.  Thus, the views are crazy in the sense defined.  If the same holds for all viable interpretations of quantum mechanics, then crazyism would be warranted in that domain.[4]

I will argue below that crazyism is warranted in the metaphysics of mind.  I will argue any well developed materialist metaphysics will be crazy, in the intended sense of the term.  I will argue the same for any well developed dualist metaphysics.  And the same for idealism (well developed or not).  And for positions that reject all three of these views or aim to reconcile or compromise among them.  But some metaphysical theory of this sort must be true – that is, either some form of materialism, dualism, or idealism must be true or some sort of rejection or compromise approach must be true.  So something crazy must be among the core truths in the metaphysics of mind.    




Materialism has enjoyed such a good vogue in Anglophone philosophy recently that it might not seem to be crazy.  And, indeed, it is not part of my thesis that materialism is crazy.  Rather, my thesis is that any well developed materialist metaphysics will be crazy.  Maybe materialism per se is sufficiently vague and noncommittal as to provide no shock to common sense.  However, I do think that working out the details of a materialist view will inevitably force choices among major violations of common sense, and no one conjunction of violations will merit belief over all rivals.  This is an empirical conjecture about the medium-term future.  (A hundred years from now, who knows?)

The materialist (or “physicalist”) position is difficult to characterize precisely.[5]  This might be a problem for the view – though if so, I’m inclined to think that it’s just a manifestation of a more general problem that I’ll discuss in section xii.  As a working approximation, let’s characterize materialism as the view that everything in the universe is composed of, or reducible to, or most fundamentally, material stuff, where “material stuff”  means things like elements of the periodic table and the various particles or waves or fields that interact with or combine to form such elements, whatever those particles, waves, or fields might be, as long as they are not themselves intrinsically mental.  The two historically most important competitor positions are idealism and substance dualism, both of which assert the existence of an immaterial soul.

It’s a striking sociological fact about materialism that, after a long history as a minority position, suddenly in the 1950s and 1960s a young generation of Anglophone philosophers of mind adopted it as orthodoxy – Hilary Putnam, Jerry Fodor, Daniel Dennett, David Lewis, J.J.C. Smart, Fred Dretske, Donald Davidson, John Searle[6], David Armstrong, Sydney Shoemaker, and many others.  Maybe this sudden generational shift reflected progress, like the progress of science.  It’s also possible that it was the broad swing of a pendulum.  We don’t yet have, I suspect, the historical distance to know.




Materialism per se might be contrary to common sense.

Materialism is almost certainly a minority view in our current culture and historically across human cultures.  People have a widespread, and maybe deep, tendency to believe that they are more than just material stuff.  I doubt most readers need convincing of this sociological fact, but for completeness see this note.[7]  Not all unpopular views violate common sense, however, by my definition of “common sense” (in section ii): It depends how confidently the opposing view is held.  In the case of materialism per se – that is, materialism abstractly considered, prior to theoretical choices about how to develop it – I find it difficult to gauge, without more systematic empirical evidence, how confident, stable, and widespread its rejection is among non-specialists.

Certain apparent consequences of materialism per se might be robustly bizarre.  This would explain anti-materialist philosophers’ fondness of these consequences as an argumentative lever.  Consider Leibniz’s mill:

Moreover, we must confess that the perception, and what depends on it, is inexplicable in terms of mechanical reasons, that is, through shapes and motions.  If we imagine that there is a machine whose structure makes it think, sense, and have perceptions, we could conceive it enlarged, keeping the same proportions, so that we could enter into it, as one enters into a mill.  Assuming that, when inspecting its interior, we will only find parts that push one another, and we will never find anything to explain a perception (1714/1989, p. 215 [§ 17], emphasis in original).

When the view is so vividly displayed, something in most people, I think, resists the materialist’s reduction of experience to bumping matter.  If you see nothing bizarre in Leibniz’s mill, maybe science and philosophy have stolen a bit of your common sense.  Other thought experiments work similarly.  Consider “zombies”: It seems we can conceive of entities physically and behaviorally identical to us but entirely lacking conscious experience or “phenomenology”.[8]  Conceivability may or may not imply possibility; the thought experiment has power regardless.  It draws the mind to think that materialism leaves something out.  Consider also Frank Jackson’s (1986) “Mary”, the super-scientist confined to a black and white room, who can seemingly learn all the physical facts about the world, including about the physics and physiology of color perception, yet remain ignorant of some experiential facts, such as what it’s like to see red.  Such thought experiments seem to tap into a folk psychological “explanatory gap” between physical properties or events and the colorful phenomenology of conscious experience; people seem to seek something immaterial to bridge the two.[9]  Maybe, then, it’s part of common sense to suppose that any materialist metaphysics will be incomplete.



Regarding materialism per se, I think it’s unclear exactly where the boundaries of common sense lie.  However, I believe that any well developed materialist metaphysics of mind – that is, any plausible materialist metaphysics with specific commitments about the necessary and sufficient conditions for possessing mental states – will inevitably astound common sense.  If it seems otherwise in reading Putnam or Lewis or Smart, that’s because materialist philosophers are often vague on the issues from which bizarreness springs.

If materialism per se conflicts with majority belief and presents a seeming explanatory gap, all the more so, it seems likely, will specific materialist accounts of consciousness.  Francis Crick (1994), for example, equates human consciousness with synchronized 40-hertz oscillations in the subset of neurons corresponding to an attended object.  Nicholas Humphrey (1992, 2011) equates consciousness in general with reentrant feedback loops in an animal’s sensory system.  Such views are not just tepidly unintuitive.  Crick and Humphrey both repeatedly emphasize that non-specialists vigorously resist their views.  Common sense fights them hard.  Common sense fights them hard not because of the details, I suspect, but rather because the details vividly reveal the bizarreness of the general project.

Another reason to anticipate sharp conflicts between common sense and well developed forms of materialism is that, as I mentioned in section i, common sense has tended to fare poorly beyond practical contexts.  A dismal induction suggests that common sense will be grossly wrong about some major aspect of the metaphysics of mind too – especially if we consider implications beyond the usual run of daily life, implications for pathological and science fiction and deep-sea cases.  Philosophers friendly to materialism should be eager, like Crick and Humphrey, to abandon poorly founded aspects of common sense.[10]

Early returns in the experimental study of folk attributions of mental states to corporations, robots, and peculiar entities suggest that folk psychology is not a paradise of rigorously principled materialism.[11]  Materialists have reason to suspect serious flaws in the folk psychological materials from which commonsense judgments must ultimately be constructed.  For example, Brian Fiala, Adam Arico, and Shaun Nichols (forthcoming) argue for a dual-process explanation of the folk psychology of consciousness attribution.  They postulate a “low road” cognitive process that attributes consciousness to entities with eyes, non-inertial motion trajectories, and apparently contingent interaction, and they postulate a “high road” cognitive process grounded in deliberate reasoning, including consciously endorsed theories.  Suppose this dual-process model is broadly correct.  One might doubt that either the low-road or the high-road process will map nicely onto any plausible well developed materialist metaphysics.  Even if one process does by happy circumstance map well, the other process – or still some third cognitive mechanism, maybe one grounded more directly in social and emotional processes – might well still prove powerful enough to generate conclusions contrary to the first and yet felt to have the force of common sense.

I will now illustrate by discussing two specific issues on which I suspect well developed materialist views will be forced into bizarreness.

First illustration of the likely bizarreness of materialism: Mad pain, Martian pain, and beer can pain.  Who in the universe can feel pain?  To judge from the literature, there are currently four viable materialist answers: beings with brains like our own, beings that react to the world in patterns similar to our own, some hybrid view, or some further-mysterious-property view.  To evoke a further mysterious property is not to have a well developed view in the sense I intend, so let’s set such gestures aside.  The remaining three views all appear to have bizarre consequences.  To insist on brains, that is, on similarity to our own interior biophysical configuration, seems terribly chauvinistic if we hope to have the whole universe in view and not just our little section of it: Couldn’t a being – an octopus or a space alien? – feel pain despite stark interior differences from us?[12]  Suppose space aliens arrive tomorrow.  They decode English from our television broadcasts and converse fluently with us, behaving much as we do – including withdrawing, screaming, writhing, protesting, avoiding, and revenging when damaged with sharp objects.  They write novels and medical treatises about their agonies, and there’s no reason to doubt their sincerity.  They look and act much like us, but inside, they operate by hydraulics, or lasers, or maybe even via the interaction of a billion writhing bugs.  I venture that it would seem bizarre to most people – a weird philosopher’s quibble – to insist that to really be experiencing pain they must also have brains like our own.  One can imagine the outraged charges of speciesism if a human were to insist that only we genuinely have conscious experiences and the aliens (perhaps now integrated into schools and marriages) are mere machines all dark inside.

As I’ve described the case, these aliens are functionally similar to us, similar in having pain states that play human-like causal roles in their mental economies.  Thus functionalism beckons: Maybe the beings in the universe who experience pain are just the beings in the universe who have states that play the causal role of pain, however those states are physically constituted.  But such functionalism also has bizarre consequences, as highlighted by Ned Block (1978/1991) and John Searle (1980, 1984, 1992).  If mentality is all about causal role, then weird assemblies of beer cans and wire, powered by windmills and controlling a marionette, could presumably have conscious experience if arranged the right way; and systems composed of rulebooks, slips of paper, and monolingual English speakers could understand Chinese.  Such systems could presumably, at least in principle, produce arbitrarily complex functional patterns of behavior, outwardly indistinguishable (except in speed) from the behavior of commonsensically conscious beings like dogs or babies or even adult humans.  Genuine mentality might even be possible for economic systems manipulated by wealthy hobbyists, if the fifth derivative of the balance of payments can be made to play the right abstractly defined causal role.  Similarly bizarre are some consequences on the flip side: If pain is all about causal role, then no one could feel pain without possessing some state that is playing the normal causal role of pain.  But it seems simple common sense that one person might enter an experiential state under one set of conditions and might tend to react to it in one way, while another person, or the same person later, might tend to enter the same type of experiential state under very different conditions and have very different reactions.  Madness, pathology, disability, drugs, brain stimulation, personality quirks, and maybe radical Sartrean freedom, can amply scramble, it seems, the actual and counterfactual causes and effects of any experiential state.  So while the brain-oriented view seems to be neural chauvinism, insisting that pain is all about causal role appears to be functional chauvinism.

Maybe both views are too simple.  Maybe we can thread the needle by hybridizing: Beings who experience pain are beings in states with one of a variety of possible biological or physical configurations – just those biological or physical configurations that normally play the causal role of pain, even if things sometimes aren’t quite normal.  The word “normally” here can be understood in various ways.  Maybe what matters is that the being possesses some type of physical or biological configuration that plays the required causal role in the right population (e.g., Lewis 1980).  Or maybe what matters is that the configuration played that role, or was selected to play that role, in the developmental or evolutionary history of the organism (e.g., Dretske 1995; Tye 1995, 2009).  Either way, you’re in pain because you’re in the physical state that normally plays the causal role of pain for you or for your group, regardless of whether that state happens to be playing exactly that role for you right this instant.

What’s central to all such appeals to normality is that pains no longer “supervene” locally: Whether you’re in pain now depends on how your current biophysical configuration is seated in the broader universe.  It depends on who else is in your group or on events in the past.  If normality turns upon the past, then you and I might be molecule-for-molecule identical with each other now, screaming and writhing equally, equally cursing our maker, but because of differences in personal or evolutionary history, you’re in pain and I’m not.  This would seem to be action at a historical distance.  If pain depends, instead, on what is currently normal for your species or group, that could change with selective genocide or with a speciation event beyond your ken.  Strange forms of anesthesia!  While local nonsupervenience is plausible for relational properties – whether I have an uncle, whether I’m thinking of coffee cup A or qualitatively identical coffee cup B – it is bizarre for pain.

The issue appears to present a trilemma for the materialist: Either accept neural chauvinism (no Martian pain), accept flat-footed functionalism (beer can pain and no mad pain), or deny local supervenience (anesthesia by speciation or genocide).  Maybe some materialist view can evade all three horns; they don’t seem logically exhaustive.  But if so, I don’t see the view out there yet.  It is, I think, a reasonable guess that no plausible, well developed materialist view can simultaneously respect all our commonsense judgments about this cluster of issues.[13]

Second illustration of the likely bizarreness of materialism: The consciousness of the United States.  It would be bizarre to suppose that the United States has a stream of conscious experience distinct from the conscious experiences of the people who compose it.  I hope you’ll agree.[14]  (By “the United States” here, I mean the large, vague-boundaried group of people who are compatriots, sometimes acting in a coordinated manner.)  Yet it’s unclear by what materialist standard the United States lacks consciousness.  Nations, it would seem, represent and self-represent.  They respond (semi-)intelligently and self-protectively, in a coordinated way, to opportunities and threats.  They gather, store, and manipulate information.  They show skillful attunement to environmental inputs in warring and spying on each other.  Their subparts (people and subgroups of people) are massively informationally interconnected and mutually dependent, including in incredibly fancy self-regulating feedback loops.  These are the kinds of capacities and structures that materialists typically regard as the heart of mentality.[15]  Nations do all these things via the behavior of their subparts, of course; but on materialist views individual people also do what they do via the behavior of their subparts.  A planet-sized alien who squints might see individual Americans as so many buzzing pieces of a somewhat diffuse body consuming bananas and automobiles, invading Iraq, exuding waste.

Even if the United States still lacks a little something needed for consciousness, it seems we ought at least hypothetically to be able to change that thing, and so generate a stream of experience.  We presumably needn’t go nearly as far as Block does in his famous “Chinese nation” example (1978/1991) – an example in which the country of China implements the exact functional structure of someone’s mind for an hour – unless we suppose, bizarrely, that consciousness is only possible among beings with almost exactly our psychology at the finest level of functional detail.  If we are willing to attribute consciousness to relatively unsophisticated beings (frogs? fish?), well, it seems that the United States can, and does sometimes, act with as much coordination and intelligence, if on a larger scale.  Arguably, the United States is vastly more functionally sophisticated than such organisms, or even than individual human beings, considering the layers upon layers of bureaucratic military and civilian organization and the subsumption of individual human intelligences within the goals and outputs of those organizations.

The most plausible materialistic attempt I’ve seen to confine consciousness within the skull while respecting the broadly functionalist spirit of most materialism is Andy Clark’s (2009) and Chris Eliasmith’s (2009) suggestion that consciousness requires the functional achievements possible through high bandwidth neural synchrony.  However, it’s hard to see why speed per se should matter.  Couldn’t conscious intelligence be slow-paced, especially in large entities?  And it’s hard to see why synchrony should matter either, as long as the functional tasks necessary for intelligent responsiveness are successfully executed.

Alternatively, one might insist that specific details of biological implementation are essential to consciousness in any possible being – for example, specific states of a unified cortex with axons and dendrites and ion channels and all that – and that broadly mammal-like or human-like functional sophistication alone won’t do.  However, as I argued regarding pain, it seems bizarrely chauvinistic to regard consciousness as only possible in beings with internal physical states very similar to our own, regardless of outwardly measurable behavioral similarity.  Or is there some specific type of behavior that all conscious animals exhibit but that the United States, perhaps slightly reconfigured, could not exhibit, and that is a necessary condition of consciousness?  It’s hard to see what that behavior could be.  Is the United States simply not enough of an “entity” in the relevant sense?  Well, why not?  What if we all held hands?

In his classic early statement of functionalism, Putnam (1965) simply rules out, on no principled grounds, that a collection of conscious organisms could be conscious.  He didn’t want his theory to result in swarms of bees having collective conscious experience, he says.  But why not?  Maybe bee swarms are dumber and represent less than do individual bees – arguably committees collectively act and collectively represent less than do their members as individuals – but that would seem to be a contingent, empirical question about bees.  To rule out swarm consciousness a priori, regardless of swarm behavior and swarm structure, seems mere prejudice against beings of radically different morphology.  Shouldn’t a well developed materialist view eventually jettison unprincipled folk morphological prejudices?  We resist, perhaps, attributing consciousness to noncompact beings and to beings whose internal mechanisms we can see – but most materialist theories appear to imply, and probably part of common sense also implies, that such differences aren’t metaphysically important.  The materialist should probably expect that some entities to which it would seem bizarre to attribute conscious experience do in fact have conscious experience.  If materialism is true, and if the kinds of broadly functional capacities that most materialists regard as central to conscious mentality are indeed central, it may be difficult to dodge the conclusion that the United States has its own stream of conscious experience, in addition to the experiences of its individual members.[16]

That’s the kind of bizarreness I’m talking about.  These two examples illustrate it, but if one or both examples fail, I hope that the general point is still plausible on broad, inductive grounds.  The more we learn about cosmology, microphysics, mathematics, and other such foundational matters, both cosmic and a priori, the grosser the violations of common sense seem to become.  The materialist should expect no lesser weirdness from the metaphysics of mind.




One alternative to materialism is dualism, the view that people are not wholly material entities but rather possess immaterial souls in addition to their material bodies.[17]  (By “dualism”, unqualified, I mean substance dualism, which posits an immaterial soul.  “Property dualism” I will discuss briefly below.)  Although dualism has merits as a first pass at a commonsense metaphysics of mind, from the 17th century to the present, the greatest philosophers of the Western world have universally found themselves forced into bizarre views when attempting to articulate the metaphysics of immateriality.  I regard this history as significant empirical evidence that a well developed metaphysics of substance dualism will unavoidably be bizarre.

Attempts at commonsense dualism founder, it seems, on at least two broad issues: the causal powers of the immaterial mind and the class of beings with immaterial minds.

The causal powers issue can be posed as a dilemma: Does the immaterial soul have the causal power to affect material entities like the brain?  If yes, then material entities like neurons must be regularly and systematically influenced by immaterial events.  A neuron must be caused to fire not just because of the chemical, electrical, and other physical influences on it but also because of immaterial happenings in spiritual substances.  And that forces a subsidiary choice.  Maybe events in the immaterial realm transfer some physical or quasi-physical push that makes the neuron behave other than it would without that immaterial push.  But that seems contrary to both ordinary ideas and mainstream scientific ideas about the sorts of events that can alter the behavior of small, material, mechanistic-seeming things like the subparts of neurons.  Alternatively, maybe the immaterial somehow causally operates on the material despite the fact that material events would transpire in exactly the same way absent that influence.  And that seems at least as strange a view.  Suppose, then, the other horn of the dilemma: The immaterial soul has no causal influence on material events.  If immaterial souls do anything, they engage in rational reflection.  On a no-influence view, such rational reflection could not causally influence the movements of the body.  You can’t make a rational decision that has any effect on the physical world.  This again seems bizarre by the standards of ordinary common sense.  I’ve rolled quickly here over some complex issues, but I hope that the informed reader will find that it rings true to say that dualists have perennially faced trouble accommodating the full range of commonsense opinion on mental-physical causation, for approximately the reasons outlined.[18]

The scope of mentality issue can be expressed as a quadrilemma.  Horn 1: Only human beings have immaterial souls.  Only we have afterlives; only we have religious salvation.  There’s a religious cleanliness to the idea.  But if the soul is the locus of conscious experience, then this view has the result that dogs are mere machines, with no consciousness, no pains, no sense experiences; there’s nothing it’s like to be a dog, any more than there’s something it’s like to be a toy robot.  And that seems bizarre.  Horn 2: Everybody and everything is in: humans, dogs, frogs, worms, viruses, carbon chains, lone hydrogen ions in outer space – we’re all conscious!  That view seems bizarre too.  Horn 3: There a line in the sand.  There’s a sharp demarcation somewhere between beings with conscious experiences and those with no conscious experiences.  But that seems weird, too: Across the spectrum of animals there’s a smooth gradation of psychological capacities.  Given this smooth gradation, how could there be a sharp line between the ensouled and unensouled creatures?  What, toads in, frogs out?  Grasshoppers in, crickets out?  If the immaterial soul is the locus of conscious experience, it ought to do some work; there ought to be big psychological differences between creatures with and without souls.  But the only remotely plausible place it seems, to draw a sharp line is between human beings and all the rest – but that puts us back on Horn 1.  Horn 4: Maybe we don’t have to draw a sharp line.  Maybe having a soul is not an on-or-off thing.  Maybe there’s a smooth gradation of ensoulment, so that some animals – frogs? – kind-of-have immaterial souls.  But that’s weird too.  What would it mean, to kind of have or halfway have an immaterial soul?  Isn’t an immaterial soul the kind of thing you either have or don’t have?  Immateriality doesn’t seem like one of these vague properties, like being red or being tall, of which there are gradations and in-between cases.[19]

I don’t intend the arguments of the past two paragraphs as a priori metaphysical arguments against dualism.  Rather, they constitute a proposed diagnosis of an empirically observed phenomenon: the failure of Descartes, Malebranche, Spinoza, Leibniz, Bayle, Berkeley, Reid, Kant, Hegel, Schopenhauer, et al., up to and including recent substance dualists like Popper and Eccles (1977) and Foster (1991) to develop non-bizarre views of the metaphysics of immateriality.  Some of these thinkers are better described as idealists or compromise/rejection theorists than substance dualists, but the mire of issues they faced was the same, and my explanation of their attraction to bizarre metaphysics is the same: Common sense opinion about immateriality is a jumble.

You might feel that there exists a well developed substance dualist metaphysics that violates common sense in no major respect.  I can’t treat every philosopher on a case-by-case basis, but let me briefly mention two: Reid, who enjoys some reputation as a commonsense philosopher, and Descartes, whose interactionist substance dualism has perhaps the best initial intuitive appeal.

Reid’s explicit and philosophically motivated commitment to common sense often leads him to refrain from advancing detailed metaphysical views – which is of course no harm to my thesis.  However, in accord with my thesis, on those occasions where Reid does develop views on the metaphysics of dualism, he appears unable to sustain his commitment to common sense.  On the scope of mentality, Reid is either silent or slides far down toward the panpsychist end: He attributes immaterial souls to vegetables (esp. in 1774-1778/1995, 3.X), but it’s unclear whether Reid thinks such immateriality is sufficient for mentality (leading to a view of mentality as radically abundant) or not (in which case Reid did not develop a criterion for non-human mentality and so his view is not “well developed” in the relevant sense).  On causal powers, Reid holds material events to be causally epiphenomenal: Only immaterial beings have genuine causal power.  Physical objects cannot produce motion or change, or even to cohere into shapes, without the regular intervention of immaterial beings (1774-1778/1995; 1788/2010).  Reid recognizes that this view conflicts with the commonsense opinions of ordinary people – though he says this mistake of the “vulgar” does them no harm (see 1788/2010, IV.3).  Despite his commitment to common sense, Reid explicitly acknowledges that on some issues human understanding is weak and common sense errs (see also 1785/2002, I.1).

Descartes, too, can’t quite keep friendly to common sense regarding causal powers and animal souls.  He advocates an interactionist dualist approach to causal powers on which activities of the soul can influence the brain.  This view is, perhaps, somewhat less jarring to common sense than some of the other options.  But interactionist dualism does, as noted above, suggest a rather odd and seemingly unscientific view of the behavior of neurons, which is perhaps part of why so many of Descartes’s dualist successors rejected interactionism.  It also, perhaps, requires some contortions to explain how the rational, non-embodied processes of the immaterial soul can be hijacked by drugs and alcohol.[20]  On the distribution of immaterial souls, Descartes occupies the extreme opposite pole from the panpsychist: Only human beings have minds.  Non-human animals, despite their evident similarity to human beings in physiology and in much of their behavior, have no more thought or sensory experience than does a cleverly made automaton (1649/1991).  That Descartes’s opponents could imagine Descartes, in Leiden, flinging a cat out a window as he asserts that animals are mere machines, is testament to the sharp division between Descartes’s and the common person’s view about the consciousness of cats.  The defenestration of the cat is, or is intended to be, the very picture of metaphysical craziness.[21]  Descartes’s interactionist dualism, on inspection, is no great monument of common sense.

I conclude that we have good grounds to believe that any well developed dualist metaphysics of mind will conflict sharply with common sense on some central issues.




The third historically important position is idealism, the view that there is no material world at all but only a world of minds or spirits, in interaction with each other or with God, or wholly solipsistic.  In the Western tradition, Berkeley (1710-1713/1965), Fichte (1794/1795/1970), and maybe Hegel (1807/1977) are important advocates of this view; some non-Western and mystical thinkers also appear to embrace idealism.[22]  As Berkeley acknowledges, idealism is not the ordinary view of non-philosophers: “It is indeed an opinion strangely prevailing amongst men that houses, mountains, rivers, and, in a word, all sensible objects have an existence, natural or real, distinct from their being perceived by the understanding” (PHK §4).  No one, it seems, is born an idealist.  They are convinced, against common sense, by metaphysical arguments or by an unusual religious or meditative experience.  Idealism also inherits the bizarre choices about causation and the scope of ensoulment that trouble dualist views: If a tree falls, is this somehow one idea causing another, in however many or few minds happen to observe it?  Do non-human animals exist only as ideas in our minds or do they have minds of their own; and if the latter, how do we avoid the slippery slope to panpsychism?

The bizarrenesses of materialism and dualism may not be immediately evident, manifesting only when details are developed and implications clarified.  Idealism, in contrast, is bizarre on its face.




There might be an alternative to classical materialism, substance dualism, or idealism; or there might be a compromise position.  Maybe Kant’s transcendental idealism (1781/1787/1998) is such an alternative or compromise, or maybe some sort of Russellian (1921, 1927) or Chalmersian (1996) neutral monism or property dualism is.  However, I think we could hardly accuse Kant, Russell, or Chalmers of articulating a commonsense view of the metaphysics of mind, even if there are aspects of their views that accord better with common sense than do some of the competitor views.  Chalmers, for example, offers no good commonsense answer to the problems of immaterial causation and the scope of immateriality, tentatively favoring epiphenomenalism and panpsychism: All information processing systems, even thermostats, have conscious experience or at least “proto-consciousness”, but such immaterial properties play no causal role in their physical behavior.  The attractions of Kant, Russell, and Chalmers lie, if anywhere, in their elegance and rigor rather than their commonsensicality.

Alternatively, maybe there’s no metaphysical fact of the matter here.  Maybe the issue is so ill-conceived that debate about it is hopelessly misbegotten (Carnap 1928/1967, 1932/1959; maybe Searle 1992, 2004[23]).  Or maybe asking metaphysical questions of this sort takes us too far beyond the proper bounds of language use to be meaningful.[24]  But this type of view, too, seems bizarre.  The whole famous mind-body dispute is over nothing real, or nothing it makes sense to try to talk about?  There is no fact of the matter about whether something in you goes beyond the merely physical or material?  We can’t legitimately ask whether some immaterial part of you might transcend the grave?  It’s one thing to allow that facts about transcendent existence might be unknowable – an agnostic view probably within the bounds of common sense options – and it’s one thing to express the view, as some materialists do, that dualists speak gibberish when they invoke the immaterial soul; but it’s quite another thing, a much more radical and unintuitive thing, to say that there is no legitimate sensible interpretation of the dualist-materialist(-idealist) debate, not even sense enough to allow the materialist coherently to express her rejection of the dualist’s transcendent hopes.




I am making an empirical claim about the history of philosophy and offering a psychological explanation for this putative empirical fact.  The empirical claim is that all existing well developed accounts of the metaphysics of mind are bizarre.  The psychological explanation is that common sense is incoherent with respect to the metaphysics of mind.  Common sense, and indeed I think simple logic, requires that one of four options be true: materialism, dualism, idealism, or a compromise/rejection view.  And yet common sense conflicts with each option, either on its face or implicitly as revealed when metaphysical choices are made and implications pursued.  If common sense is indeed incoherent in the metaphysics of mind, then the empirical claim can be modally generalized: It is not possible to develop a metaphysics of mind that is both coherent and non-bizarre by the standards of current common sense, if that view involves specific commitments on tricky issues like fundamental ontology, mind-body causation, and the scope of mentality.  Call this thesis universal bizarreness.

Crazyism requires conjoining universal bizarreness with a second thesis, universal dubiety, to which I will now turn.  The universal dubiety thesis is just the thesis that none of the bizarre options compels belief.

What is it for a position to be dubious, or – equivalently, as I intend – for it to fail to compel belief?  In previous drafts, I’ve sketched it differently, but epistemic psychology of dubiety and belief compulsion is a distractingly thorny affair.  Instead of trying to hone it to a fine point, let me suggest that the arguments below are robust across conceptualizations of dubiety.  If the arguments work, they jointly (and perhaps severally) deliver the conclusion that materialism is a dubious metaphysical position, and so also are dualism, idealism, and compromise/rejection views, for most ways of conceptualizing dubiety.

They do, that is, unless one insists on a high bar for dubiety (a low bar for compulsion).  If, for example, it were sufficient for a position to be “compelled” and “non-dubious” that a well-informed person could rationally regard that position as slightly more likely to be true than false – then one of the four broad metaphysical perspectives might fail to be “dubious”.  I wouldn’t insist, for example, that everyone must invest exactly 25% of their subjective credence in each of materialism, dualism, idealism, and compromise/rejection.  Maybe it would be warranted to regard one of these positions as more likely to be true than some of the others – even perhaps a bit more likely than the other three positions combined.  But I would insist that for the philosophical community as a whole and for most of the people I imagine reading this essay, it wouldn’t be epistemic good judgment, for the reasons I am about to describe, to invest a lot of confidence in any one of these four positions.  And I would also suggest that there exists a somewhat finer slicing of the options – with, say, three substantially different variants of each of the four main classes of position – such that no one moderately finely sliced position warrants community acceptance as more likely to be true than false.

Let me be clear, too, that I make no claims about the distant future, but only the near to medium term – the foreseeable future or the next few decades.  Boldly extrapolating lines of technological progress, in a hundred years things might look very different.  Maybe “the singularity” will have arrived (Kurzweil 2005), and our vastly cognitively superior descendants will laugh good-naturedly at our monkey-mindedness, impressed that beings barely able to pass the Wason Selection Task (Wason and Johnson-Laird 1972) could have generated as much scholarship as we did.  Or maybe we will have invented high-bandwidth aerial neural transducers that enable dozens or thousands or millions of brains to interact as intimately as your right and left hemispheres now interact (Churchland 1981).  Common sense and our epistemic situation might change radically.  About the 22nd century, I hazard no guesses.




An Argument from Authority and Maybe Peers.

Let’s assume that you, reader, are not among the world’s leading metaphysicians of mind.  And let’s assume that you’re drawn toward some particular metaphysics of mind other than David Chalmers’s property dualism.  It seems likely that David Chalmers, who is one of the world’s leading metaphysicians of mind, and who is by all accounts highly intelligent and well read, could run argumentative rings around you, including pointing out relevant considerations of which you are now unaware.  Any unbiased referee would call a knockout in the first or second round.  Given that fact, how confident should you be in your opinion?  Or suppose you’re drawn toward something like the Chalmers view after all.  Likely David Lewis could have run rings around you, defending his version of materialism.  Last spring, I described various metaphysical options to my then eleven-year-old son (yet another David).  Davy immediately adopted one position against all others, and he refused to be budged by my counterarguments.  It seems a kind of epistemic failing – although also, in a different way, a kind of intellectual virtue that will serve him well in his education – for Davy to be confident in his view.  He barely even understood the issues, much less had a deep appreciation of the arguments.  If you or I stand confidently against the giants, armed only with our weaker comprehensions, are we so different from Davy?  Some of us might happen to have the right view, maybe even because we are sensitive, as others of us are not, to the real considerations that decisively favor it; but in some epistemically important sense that’s just luck.

Suppose that’s a fair assessment of the epistemic situation in your own case in particular.  What should you do about it?  Read enough philosophy to become one of the world’s leading metaphysicians?  Even if that were practical, it wouldn’t settle what your attitude should be right now, which is the question.  Should you simply, then, bow to expert opinion, as one might bow to the expert opinion of a chemist about the electronegativity of fluorine?  That doesn’t seem right either.  For one thing, there is no consensus expert opinion to bow to.  For another, on an issue as central to one’s worldview as mind and body (especially because of its connection to religious belief), and as subject to preconception and bias even among experts, it may be wise not to cede one’s intellectual autonomy.  I recommend this instead: Acknowledge dubiety.  If you favor materialism, favor it fearfully.  If you favor one particular form of materialism, spread your confidence distribution broadly enough that your credence in that view does not exceed your estimation of the likelihood of all other competing positions combined.  For those of us who are not among the world’s leading metaphysicians of mind, I submit that this is the sweet spot between autonomous self-confidence and appropriate intellectual humility.

If I’m fortunate, some readers will be among the world’s leading metaphysicians of mind.  To you, this argument does not apply.  However, there might be a parallel argument cast in terms of disagreement among epistemic peers.[25]

Probably, on empirical grounds, we ought to regard each of the four broad metaphysical options as rather dubious, and we ought to regard more specific positions within those four broad options as substantially more dubious.  By “we” I mean the philosophical community as a whole and most of the notional readership of this essay.  For us, implacable, long-term disagreement among the best-informed experts, with no one option accepted by a majority of experts and no foreseeable hope of resolution, is good reason to accept the universal dubiety thesis.

The present argument might seem to generalize to most of philosophy.  I’m inclined to think it does generalize, but not as much one might think.  In areas of progress and discovery (logic, historical interpretation, evaluation of the consequences of specific argumentative moves, empirically driven inquiries, newly opened issues) the peers version, at least, breaks down: One might have good grounds for thinking oneself early to the discovery.  And perhaps non-experts, too, can avail themselves of those same grounds.  The argument will also fail to generalize to issues on which pluralism is warranted – cases in which multiple conflicting approaches can have approximately equal merit, such as perhaps in the articulation of visions of the good life or in goal-relative pragmatic recommendations for the adoption of particular conceptual structures.  What’s left, perhaps, are only the grand, timeless, factual disputes that continually defy us and on which expert opinion is highly divergent.  Such disputes are few.

Is this argument objectionably authoritarian or defeatist?  I hope not.  I am not saying: You’re not entitled to an opinion where the experts (or your peers) disagree.  One may still have a favored view.  I hope you do.  One might even “accept” that view, in the pragmatic sense of treating the view as a basis for action and further reflection.[26]  I advise not deference or despair but rather autonomy thoroughly salted with a sense of one’s limitations.  The failures of millennia of philosophical ambition, and the discord among thousands of currently-living PhD’s, should humble us all.




A No-Method Argument.

There is no conscious-ometer.  Nor should we expect one soon.  There is also no material-world-ometer.  The lack of these devices problematizes the metaphysics of mind.

Samuel Johnson kicked a stone.  Thus, he said, he refuted Berkeley’s idealism (Boswell 1791/1980, p. 333).  Johnson’s proof convinces no one with an inkling of sympathy for Berkeley, nor should it.  Yet it’s hard to see what empirical test could be more to the point.  Carnap (1928/1967, p. 333-334) imagines an idealist and a non-idealist both measuring a mountain; there is no experiment on which they will disagree.  No multiplicity of gauges, neuroimaging equipment, or particle accelerators could give stronger empirical proof against idealism than Johnson’s kick.  Similarly, Smart, in his influential defense of materialism, admits that no empirical test could distinguish materialism from epiphenomenalist substance dualism (1959, p. 155-156); there is no epiphenomenal-substance-ometer.

Why, then, should we be materialists?  Smart appeals to Occam’s razor: Materialism is simpler.  But simplicity is a complex business.[27]  Arguably, Berkeley’s idealism is simpler than either dualism or materialism and solipsism is simpler yet.  And anyhow, simplicity is at best one theoretical virtue among several, to be balanced in the mix.  Abstract theoretical virtues like simplicity will, I suggest, attach only indecisively, non-compellingly, to the genuine metaphysical contenders.  I’m not sure how to argue for this other than to invite you sympathetically to feel the abstract beauties of some of the contending views other than your favorite.

If we’re willing to commit to materialism, we might still hope at least for a conscious-ometer that we could press against a human or animal head to decide among, say, relatively conservative vs. moderate vs. liberal materialistic views of the abundance or sparseness of consciousness in the world.  But even this is too much to hope for, I think, in the near to medium term.  Is a frog conscious?  That is, does a frog have a stream of phenomenal experience?  Is there something it’s like to be a frog?  If two theorists of consciousness disagree about this matter, no output from an fMRI machine is likely to resolve their disagreement – not unless they share much more in common than generally is shared by conservatives and liberals about the abundance of consciousness.  Nor can a frog report its experience or lack of experience in any straightforward way.  Similarly intractible, I think, is the dispute about how richly detailed human experience is – about whether, for example, people have constant tactile experience of their feet in their shoes.[28]  If such disputes are intractable, we have no firm grounds of choice between approaches to consciousness that are relatively liberal (perhaps even as liberal as panpsychism) and approaches that are relatively conservative (perhaps even as conservative as restricting consciousness to adult human beings in their more self-aware moments).  Nor, I think, do we have good grounds to deny that liberal and conservative views constitute very different metaphysical pictures.  Maybe some disputes among materialists are merely terminological (certain forms of functionalism vs. certain forms of identity theory?).  Not the abundance dispute, though; at least not always.  Either there’s something it’s like to be a frog, or there isn’t, or somewhere in-between, or the question is somehow broken.  These are substantially different positions, each with some ineliminable plausibility and no broadly acceptable means of empirical test.

Thus I suggest: Major metaphysical issues of mind are resistant enough to empirical resolution that none compel belief on empirical grounds, and none, at a moderate grain of specificity, warrant a degree of credence exceeding that of all competitors; and this situation is unlikely to change in the foreseeable future.  Neither do these issues permit resolution by appeal to common sense (which will rebel against all and is probably a poor guide anyway), by appeal to broad, abstract theoretical considerations, or by appeal to the consensus judgment of well-trained philosophical experts.  I assume there are no logical self-contradictions in any of these views, at least insofar as they are well developed real contenders.

Is there some other means of settling the matter that I’m overlooking?




An Argument from Cosmological Crazyism.

If a broad-reaching cosmological crazyism is true, then crazyism in the metaphysics of mind is a natural consequence.  If we don’t know how the universe works, we don’t know how the mind fits within it.

I can’t defend cosmological crazyism in detail here, but a few remarks can highlight its plausibility.  Consider the bizarreness of quantum theory and the lack of consensus about its interpretation, including the fact that some interpretations treat mentality as fundamental (such as the many minds view and some versions of the Copenhagen interpretation[29]).  Consider the bizarreness of relativity theory, perhaps especially the relativistic concept of distance, and the apparent willingness of at least a small portion of the physics community in 2011 to contemplate its overthrow given a single report of apparently faster-than-light neutrinos.[30]  Consider, too, the apparent conflict between relativity theory and quantum theory.[31]  Consider that many cosmologies now posit either a creator who set the physical constants or initial conditions at the time of the Big Bang so as to support the eventual occurrence of life, or a vastly unlikely chance setting of those variables, or some sort of dependence of the universe upon our observation of it, or the real existence of a vast number of universes (or aeons of this universe) with different physical constants.[32]  The last of these four views – broadly, multiverse theory – seems to be a recent favorite.  Prima facie, multiverse theory is both dubious and bizarre.  Here’s one among the bizarrenesses: If the number of universes is infinite, or if there is even a single infinite universe of the right sort, then every event of finite probability will occur an infinite number of times (given certain background assumptions about cosmic diversity).  The spontaneous congealment, from relatively disorganized matter, of a molecule-for-molecule twin of any living person is often held to have a very tiny but finite probability.[33]  You would, then, be one among an infinite number of actually existing molecule-for-molecule twins of yourself, of diverse origin.  (Shades of Nietzsche’s eternal return?)  Quantum cosmology has also been interpreted as suggesting the backward causation of the history of the universe by our current acts of scientific observation (e.g., Hawking and Mlodinow 2010, p. 140).

Shall we look, then, to religion for non-bizarre cosmologies?  That seems an unlikely source.  Creation stories, accounts of the afterlife – especially in the hands of those who would attempt to work out the full ontological implications – seem only a source of further bizarreness.

Another difficulty is this: If consciousness can be created within artificial networks manipulated by external users – for example in computer programs run by children for entertainment – and if the beings inside those networks can be kept ignorant of their nature, then there could be beings in the universe who are vastly deluded in fundamental matters of metaphysics.  Such beings, perhaps, might think they live in a wide world of people like them when in fact they have three-hour lives, isolated from all but their creator and whatever other beings are instantiated in the same artificial environment.  There is, I think, a non-negligible possibility that we (I?  you?) are such beings.[34]  Suppose in the year 2200 a new computer game is released, Sims 2012, and it’s a huge hit.  A hundred million children buy it.  Each instance of Sims 2012, when run, creates a hundred thousand actually conscious simulated people, each of whom thinks she is living in the early 21st century and has an appropriate range of apparent memories and apparent sensory experiences.  In reality, these people serve mainly to provide entertaining reactions when, to their surprise, Godzilla tromps through.  Possibly, if the economics of technology plays out right, there are many more such simulated beings in the universe than there are non-simulated beings.  The details don’t matter too much, whether the outside agents are children or historians or scientists, Earthly beings or gods or aliens running an Earth fiction.  Might we be Sims of broadly this sort?  To think that we are in fact Sims is, of course, crazy.  But is the possibility too crazy to figure in a disjunction of live cosmological options?  Is it more than one order of magnitude crazier than multiverse theory or the typical well developed religious cosmology?  There are no commonsense cosmologies left.

Further support for cosmological dubiety comes from our (apparently) miniscule cosmological perspective.  If mainstream scientific cosmology is correct, we have seen only a very small, perhaps an infinitesimal, part of reality.  We are like fleas on the back of a dog, watching a hair grow and saying, “Ah, so that’s how the universe works!”

There seems to me to be sufficient cosmological uncertainty to cast into doubt any metaphysics of mind with cosmological commitments.  And all well developed metaphysical accounts of the mind will have cosmological commitments, if only in the choice between materialism, dualism, idealism, or a compromise/rejection view.  For example, if it might be the case that an immaterial entity fashioned the physical constants, then we cannot justifiably rest assured that materialism is true.  If there might really exist universes (not just “possible worlds” but actual universes) so radically different from our own that cognition transpires without the existence of anything we would rightly call material, then materialism is at best a provincial contingency.  If we are created within a simulation by outside agents, our experience of objects as necessarily laid out in space and time might be a feature of our programming environment that doesn’t reflect the fundamental structure of the universe (Kant meets cyberpunk).

Scientific cosmology is deeply and pervasively bizarre; it is highly conjectural in its conclusions; it has proven unstable over the decades; and experts persistently disagree on fundamental points.  Nor is it even uniformly materialist.  If materialism draws its motivation from being securely and straightforwardly the best scientific account of the fundamental nature of things, materialists ought to think twice.  I focus on materialism, since it is the dominant view in contemporary metaphysics of mind, but similar considerations cast doubt on dualism, idealism, and compromise/rejection views.




Certain fundamental questions about the metaphysics of mind can’t be settled by science, in its current state, or by abstract reasoning.  To address these questions we must turn to common sense.  If we then have good reason to think that common sense, too, is no reliable guide, we are unmoored.  Without common sense as a constraint, the possibilities open up, bizarre and beautiful in their different ways; and once open they refuse to shut.  This is crazyism.

Does it follow that you don’t know that you are on Earth, reading philosophy?  Does crazyism collapse into radical skepticism?  No, or at least not straightforwardly.  Earth might actually be SimEarth or nothing but a constellation of ideas in the mind of God – its fundamental nature might be very different than you are inclined to suppose – but even in such transparently bizarre metaphysical or cosmological stories, Earth exists.[35]  In even more stories, the computer screen or piece of paper you are looking at exists.  Nothing I have said implies, I think, that it’s unreasonable to distribute most of your credence to Earth-involving stories over Earth-denying ones.  And then, maybe, if Earth does exist, and if your belief that it does has arisen in the right manner or has the right kind of support, you will qualify as knowing that fact.[36]



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            [1] For example, Frege 1884/1953; Lewis 1986; Yablo 1987.

            [2] Critiques of the role of common sense or philosophical intuition as a guide to metaphysics and philosophy of mind can be found in, for example, Churchland 1981; Stich 1983; Gopnik and Schwitzgebel 1998; Kornblith 1998; Dennett 2005; Ladyman and Ross 2007; and Weinberg, Gonnerman, Buckner, and Alexander 2010.  Hume 1740/1978 and Kant 1781/1787/1998 are also interesting on this issue, of course.  Even metaphilosophical views that treat metaphysics largely as a matter of building a rigorous structure out of our commonsense judgments often envision conflicts within common sense so that the entirety of common sense cannot be preserved: e.g., Ayer 1967; Kriegel 2011.

            [3] DeWitt, for example, writes:

I still recall vividly the shock I experienced on first encountering this multiworld concept. The idea of 10100+ slightly imperfect copies of oneself all constantly splitting into further copies, which ultimately become unrecognizable, is not easy to reconcile with common sense (1970, p. 33).

            [4] Recent reviews of the difficulties in settling among various bizarre interpretations include Penrose 2004; Wallace 2008.

[5] See, e.g., Hempel 1980; Chomsky 1995; Montero 1999; Stoljar 2010.

            [6] Although Searle rejects the dualism-materialism distinction, I believe he is materialist in the vague sense of the previous paragraph.  See, e.g., Searle 1995, pp. 6-7.

            [7] In the General Social Survey of Americans in 2010 (; accessed September 16, 2011), 72% of respondents reported believing in life after death and 17% reported disbelieving; also, 75% reported believing in God, 11% reported belief in an impersonal “Higher Power”, and only 3% reported atheism.  We can probably safely assume that most contemporary American theists are not materialists (though some may be: Baker 1995; Murphy 2006).  Some other industrialized Western nations are more secular than the U.S., but even in those societies religiosity is widespread (Zuckerman 2007), and religiosity or belief in entities not tolerated by materialism might even be something like a cultural universal (Brown 1991; McCauley 2000; Boyer 2001).  Paul Bloom (2004) has argued on developmental and cross-cultural grounds that it is innately natural to human beings to think of mental life as the product of an immaterial soul, even if some of us reject dualism on an “airy intellectual level” (see also Richert and Harris 2006; Hodge 2008; Slingerland and Chudek 2011).  In David Bourget’s and David Chalmers’ 2009 PhilPapers survey of faculty in leading Anglophone philosophy departments, 62% of respondents reported accepting atheism and another 11% reported “leaning toward” it.  Yet even in this remarkably secular group, only 35% reported accepting and 22% reported leaning toward physicalism (; accessed September 19, 2011).

            [8] See, e.g., Campbell 1970; Kirk 1974, 2005; Chalmers 1996.

                [9] See, e.g., Levine 1983, 2001; Chalmers 1996; Ramsey 2006; Robbins and Jack 2006.

            [10] See, e.g., Churchland 1981; Stich 1983; Metzinger 2003; Dennett 2005; Mandik and Weisberg 2008. 

            [11] Gray, Gray, and Wegner 2007; Knobe and Prinz 2008; Huebner, Bruno, and Sarkissian 2010; Sytsma and Machery 2010; Buckwalter and Phelan 2011.

            [12] This thought is central to early functionalist arguments against identity theory materialism, e.g., Putnam 1965; Fodor 1974.  For discussion and criticism see Bechtel and Munsdale 1999; Shapiro and Polger forthcoming.

            [13] See also Adams and Dietrich 2004.  See Hill 2009 for a rather different argument that the folk metaphysics of pain is incoherent.

            [14] Admittedly, the willingness of English-language speakers to ascribe mental states of various sorts to corporate entities is empirically complex.  See Knobe and Prinz 2008; Sytsma and Machery 2009; Arico 2010; Huebner, Bruno, and Sarkissian 2010.

                [15] E.g., Fodor 1987, 1990; Dennett 1987, 1991; Churchland 1984/1988; Dretske 1988, 1995; Lycan 1996; Tononi 2004; Carruthers 2005; Rosenthal 2005; Hill 2009; Humphrey 2011.  Even materialists who emphasize the identity of mental states and brain states will normally see functional or causal structures of this sort as what it is that makes brain states the kinds of states that are conscious while the internal states of, say, a toaster are not: e.g., Armstrong 1968; Bechtel and Mundale 1999.  Searle (1984, 1992) seems to be an exception to the tendency described here, though I find his positive position on the biological causes of consciousness too indeterminate in its commitments to fully evaluate on the present issue.

            [16] See also Strawson 1959, p. 113-115; Combs and Krippner 2008; Huebner 2011.  On group intentionality without (necessarily) group consciousness see Gilbert 1989; Austen Clark 1994; Rovane 1998; Bratman 1999; Wilson 2004; Tuomela 2007; Searle 2010; List and Pettit 2011; Huebner forthcoming.

            [17] “Immaterial soul” is intended here in a fairly broad but traditional sense.  By this criterion, some metaphysical systems that call themselves substance dualist, notably Lowe’s (2008), do not qualify.  Despite Lowe’s choice of label his system is very different from traditional substance dualist approaches and for current purposes is probably better conceived as a compromise position.

            [18] Patterson 2005 usefully compares historical and modern approaches to this issue.

            [19] The same quadrilemma arises if immateriality is regarded as essential to life, as on the types of vitalist theories that were discarded in the early 20th century and on immaterialist views of the “vegetative soul”.  Nor does that move resolve the core question about mentality.  As Pierre Bayle nicely articulates, even accepting something like a sharp-boundaried immaterialist vitalism about life doesn’t ameliorate this complex of issues regarding the “rational soul”, or mindedness, or conscious experience (1697/1702/1965, “Rorarius”; see also Des Chene 2006).

            [20] See especially La Mettrie (1748/1994).  The power of these two examples is that drugs and alcohol appear to affect the reasoning process itself and not only the passions and bodily movements, contra Descartes’s picture of how bodily influences can oppose the immaterial processes of reason (1649/1985, esp. §47).

            [21] See Grayling 2005, p. 135, for a recent account of this apocryphal event.

            [22] See especially the Indian Advaita Vedanta and Yogacara traditions – though these traditions present some of the same interpretative challenges as Hegel, probably involving strands better interpreted as a type of compromise or rejection view.  See Deutsch 1969/1973; Deutsch and van Buitenen, eds., 1971; Collins 1998; Lusthaus 2002; Trivedi 2005.

            [23] However, despite Searle’s self-description I would classify Searle as broadly speaking a materialist (see note ****).

            [24] This might seem a broadly Wittgensteinian position, but it’s probably not Wittgenstein’s own position; see esp. 1945-1949/1958, p. 178, and 1947/1980, vol. 1, §265.

            [25] On the epistemology of peer disagreement see, e.g., Feldman and Warfield, eds., 2010.

            [26] E.g., Van Fraassen 1980; Cohen 1992; Bratman 1999.

            [27] E.g., Hempel 1966; Sober 1975; Zellner et al., eds., 2001.

            [28] For example, Dennett 1991 vs. Searle 1992.  I suspect that most readers will find the medium-term irresolvability of this latter dispute to be less plausible prima facie than in the between-species case.  I defend my pessimism about this issue at length in Schwitzgebel 2011.

                [29] Wigner 1961; Albert and Loewer 1988; Albert 1992; Faye 2008.

            [30] Neutrino result reported in OPERA collaboration 2011.  For some scientific community reaction see Brumfiel 2011; Matson 2011.

            [31] Or at least the locality restriction central to relativity theory. See Einstein, Podolsky, and Rosen 1935; Bell 1964; Maudlin 1994/2002.

            [32] The is the “fine-tuning” issue.  See Barrow, Morris, Freeland, and Harper, eds., 2008; Hawking and Mlodinow 2010; Penrose 2010; Stenger 2011.

                [33] For discussion: Bousso and Freivogel 2007; Page 2008; Carroll 2010; De Simone, Guth, Linde, Noorbala, Salem, and Vilenkin 2010.  Such people, or brains, or people-plus-sections-of-environment, have been dubbed “Boltzmann babies” or “Boltzmann brains” after the 19th century physicist, Ludwig Boltzmann, who argued that in a universe of sufficient size any arbitrary low-entropy event – including presumably the congealment of a person – could be expected to occur by chance (e.g., Boltzmann 1897).

            [34] Bostrom 2003; also Chalmers 2010.

            [35] See Berkeley 1710-1713/1965; Chalmers 2010, ch. 13.

            [36] For helpful comments on drafts or conversation on these topics during the course of writing thanks to Ned Block, Kurt Boughan, Peter Carruthers, Becko Copenhaver, Dan Dennett, Fred Dretske, Chris Hill, Linus Huang, Bryce Huebner, Jenann Ismael, Barry Loewer, Bill Lycan, Pete Mandik, Jozef Muller, Alan Tapper, Splintered Mind readers, ****, and audiences at University of Cincinnati, ****.