Why does science reject dualism

See Averill and Keating Another response is to challenge the relevance of the conservation principle in this context. This approach has been termed conditionality , namely the view that conservation is conditional on the physical system being closed, that is, that nothing non-physical is interacting or interfering with it, and, of course, the interactionist claims that this condition is, trivially, not met. That conditionality is the best line for the dualist to take, and that other approaches do not work, is defended in Pitts and Cucu and Pitts This, they claim, makes the plausibility of interactionism an empirical matter which only close investigation on the fine operation of the brain could hope to settle.

Cucu, in a separate article , claims to find critical neuronal events which do not have sufficient physical explanation. This claim clearly needs further investigation. Robins Collins has claimed that the appeal to conservation by opponents of interactionism is something of a red herring because conservation principles are not ubiquitous in physics. He argues that energy is not conserved in general relativity, in quantum theory, or in the universe taken as a whole. Why then, should we insist on it in mind-brain interaction?

This is a very natural assumption, but it is not justified if causal overdetermination of behaviour is possible. There could then be a complete physical cause of behaviour, and a mental one. The strongest intuitive objection against overdetermination is clearly stated by Mills , who is himself a defender of overdetermination. For X to be a cause of Y , X must contribute something to Y.

The only way a purely mental event could contribute to a purely physical one would be to contribute some feature not already determined by a purely physical event.

But if physical closure is true, there is no feature of the purely physical effect that is not contributed by the purely physical cause. Hence interactionism violates physical closure after all. Mills says that this argument is invalid, because a physical event can have features not explained by the event which is its sufficient cause.

The opponent of overdetermination could perhaps reply that his principle applies, not to every feature of events, but to a subgroup — say, intrinsic features, not merely relational or comparative ones. It is this kind of feature that the mental event would have to cause, but physical closure leaves no room for this. These matters are still controversial.

The problem with closure of physics may be radically altered if physical laws are indeterministic, as quantum theory seems to assert. If physical laws are deterministic, then any interference from outside would lead to a breach of those laws. But if they are indeterministic, might not interference produce a result that has a probability greater than zero, and so be consistent with the laws?

This way, one might have interaction yet preserve a kind of nomological closure, in the sense that no laws are infringed. Because it involves assessing the significance and consequences of quantum theory, this is a difficult matter for the non-physicist to assess. Some argue that indeterminacy manifests itself only on the subatomic level, being cancelled out by the time one reaches even very tiny macroscopic objects: and human behaviour is a macroscopic phenomenon.

For discussion of this, see Eccles , , and Popper and Eccles Still others argue that quantum indeterminacy manifests itself directly at a high level, when acts of observation collapse the wave function, suggesting that the mind may play a direct role in affecting the state of the world Hodgson ; Stapp If the reality of property dualism is not to be denied, but the problem of how the immaterial is to affect the material is to be avoided, then epiphenomenalism may seem to be the answer.

According to this theory, mental events are caused by physical events, but have no causal influence on the physical. I have introduced this theory as if its point were to avoid the problem of how two different categories of thing might interact. In fact, it is, at best, an incomplete solution to this problem. If it is mysterious how the non-physical can have it in its nature to influence the physical, it ought to be equally mysterious how the physical can have it in its nature to produce something non-physical.

But that this latter is what occurs is an essential claim of epiphenomenalism. For development of this point, see Green , — There are at least three serious problems for epiphenomenalism.

First, as I indicated in section 1 , it is profoundly counterintuitive. What could be more apparent than that it is the pain that I feel that makes me cry, or the visual experience of the boulder rolling towards me that makes me run away?

At least one can say that epiphenomenalism is a fall-back position: it tends to be adopted because other options are held to be unacceptable. The second problem is that, if mental states do nothing, there is no reason why they should have evolved.

This objection ties in with the first: the intuition there was that conscious states clearly modify our behaviour in certain ways, such as avoiding danger, and it is plain that they are very useful from an evolutionary perspective. Frank Jackson replies to this objection by saying that it is the brain state associated with pain that evolves for this reason: the sensation is a by-product.

Evolution is full of useless or even harmful by-products. For example, polar bears have evolved thick coats to keep them warm, even though this has the damaging side effect that they are heavy to carry. But with mental states, dualistically conceived, the situation is quite the opposite.

The laws of physical nature which, the mechanist says, make brain states cause behaviour, in no way explain why brain states should give rise to conscious ones. The laws linking mind and brain are what Feigl calls nomological danglers , that is, brute facts added onto the body of integrated physical law.

Why there should have been by-products of that kind seems to have no evolutionary explanation. The third problem concerns the rationality of belief in epiphenomenalism, via its effect on the problem of other minds. It is natural to say that I know that I have mental states because I experience them directly. But how can I justify my belief that others have them? I know that certain of my mental states are correlated with certain pieces of behaviour, and so I infer that similar behaviour in others is also accompanied by similar mental states.

Many hold that this is a weak argument because it is induction from one instance, namely, my own. I seem to know from my own case that mental events can be the explanation of behaviour, and I know of no other candidate explanation for typical human behaviour, so I postulate the same explanation for the behaviour of others.

But if epiphenomenalism is true, my mental states do not explain my behaviour and there is a physical explanation for the behaviour of others. It is explanatorily redundant to postulate such states for others.

I know, by introspection, that I have them, but is it not just as likely that I alone am subject to this quirk of nature, rather than that everyone is?

The epiphenomenalist wishes to preserve the integrity of physical science and the physical world, and appends those mental features that he cannot reduce.

The parallelist preserves both realms intact, but denies all causal interaction between them. They run in harmony with each other, but not because their mutual influence keeps each other in line. That they should behave as if they were interacting would seem to be a bizarre coincidence.

This is why parallelism has tended to be adopted only by those — like Leibniz — who believe in a pre-established harmony, set in place by God. The progression of thought can be seen as follows. Descartes believes in a more or less natural form of interaction between immaterial mind and material body. Malebranche thought that this was impossible naturally, and so required God to intervene specifically on each occasion on which interaction was required.

Leibniz decided that God might as well set things up so that they always behaved as if they were interacting, without particular intervention being required.

Outside such a theistic framework, the theory is incredible. One category of arguments for dualism is constituted by the standard objections against physicalism. Because this argument has its own entry see the entry qualia: the knowledge argument , I shall deal relatively briefly with it here.

One should bear in mind, however, that all arguments against physicalism are also arguments for the irreducible and hence immaterial nature of the mind and, given the existence of the material world, are thus arguments for dualism. The knowledge argument asks us to imagine a future scientist who has lacked a certain sensory modality from birth, but who has acquired a perfect scientific understanding of how this modality operates in others.

Suppose that Harpo, thanks to developments in neurosurgery, has an operation which finally enables him to hear. It is suggested that he will then learn something he did not know before, which can be expressed as what it is like to hear , or the qualitative or phenomenal nature of sound. These qualitative features of experience are generally referred to as qualia. If Harpo learns something new, he did not know everything before.

He knew all the physical facts before. So what he learns on coming to hear — the facts about the nature of experience or the nature of qualia — are non-physical. This establishes at least a state or property dualism. See Jackson ; Robinson There are at least two lines of response to this popular but controversial argument. This essentially behaviouristic account is exactly what the intuition behind the argument is meant to overthrow. Such appeals to intuition are always, of course, open to denial by those who claim not to share the intuition.

Some ability theorists seem to blur the distinction between knowing what something is like and knowing how to do something, by saying that the ability Harpo acquires is to imagine or remember the nature of sound. In this case, what he acquires the ability to do involves the representation to himself of what the thing is like. But this conception of representing to oneself, especially in the form of imagination, seems sufficiently close to producing in oneself something very like a sensory experience that it only defers the problem: until one has a physicalist gloss on what constitutes such representations as those involved in conscious memory and imagination, no progress has been made.

Rather, it is new way of grasping something that he already knew. Demonstrative concepts pick something out without saying anything extra about it. Similarly, the scientific knowledge that Harpo originally possessed did not enable him to anticipate what it would be like to re-express some parts of that knowledge using the demonstrative concepts that only experience can give one.

The knowledge, therefore, appears to be genuinely new, whereas only the mode of conceiving it is novel. Furthermore, experiencing does not seem to consist simply in exercising a particular kind of concept, demonstrative or not. When Harpo has his new form of experience, he does not simply exercise a new concept; he also grasps something new — the phenomenal quality — with that concept.

How decisive these considerations are, remains controversial. I said above that predicate dualism might seem to have no ontological consequences, because it is concerned only with the different way things can be described within the contexts of the different sciences, not with any real difference in the things themselves.

This, however, can be disputed. The argument from predicate to property dualism moves in two steps, both controversial. The first claims that the irreducible special sciences, which are the sources of irreducible predicates, are not wholly objective in the way that physics is, but depend for their subject matter upon interest-relative perspectives on the world.

This means that they, and the predicates special to them, depend on the existence of minds and mental states, for only minds have interest-relative perspectives. The second claim is that psychology — the science of the mental — is itself an irreducible special science, and so it, too, presupposes the existence of the mental.

Mental predicates therefore presuppose the mentality that creates them: mentality cannot consist simply in the applicability of the predicates themselves. First, let us consider the claim that the special sciences are not fully objective, but are interest-relative. A mass of matter could be characterized as a hurricane, or as a collection of chemical elements, or as mass of sub-atomic particles, and there be only the one mass of matter.

But such different explanatory frameworks seem to presuppose different perspectives on that subject matter. This is where basic physics, and perhaps those sciences reducible to basic physics, differ from irreducible special sciences. On a realist construal, the completed physics cuts physical reality up at its ultimate joints: any special science which is nomically strictly reducible to physics also, in virtue of this reduction, it could be argued, cuts reality at its joints, but not at its minutest ones.

If scientific realism is true, a completed physics will tell one how the world is, independently of any special interest or concern: it is just how the world is. It would seem that, by contrast, a science which is not nomically reducible to physics does not take its legitimation from the underlying reality in this direct way.

Rather, such a science is formed from the collaboration between, on the one hand, objective similarities in the world and, on the other, perspectives and interests of those who devise the science. The concept of hurricane is brought to bear from the perspective of creatures concerned about the weather.

Creatures totally indifferent to the weather would have no reason to take the real patterns of phenomena that hurricanes share as constituting a single kind of thing.

With the irreducible special sciences, there is an issue of salience , which involves a subjective component: a selection of phenomena with a certain teleology in mind is required before their structures or patterns are reified. The entities of metereology or biology are, in this respect, rather like Gestalt phenomena. Even accepting this, why might it be thought that the perspectivality of the special sciences leads to a genuine property dualism in the philosophy of mind?

It might seem to do so for the following reason. Having a perspective on the world, perceptual or intellectual, is a psychological state. So the irreducible special sciences presuppose the existence of mind. If one is to avoid an ontological dualism, the mind that has this perspective must be part of the physical reality on which it has its perspective.

But psychology, it seems to be almost universally agreed, is one of those special sciences that is not reducible to physics, so if its subject matter is to be physical, it itself presupposes a perspective and, hence, the existence of a mind to see matter as psychological. If this mind is physical and irreducible, it presupposes mind to see it as such. We seem to be in a vicious circle or regress.

We can now understand the motivation for full-blown reduction. A true basic physics represents the world as it is in itself, and if the special sciences were reducible, then the existence of their ontologies would make sense as expressions of the physical, not just as ways of seeing or interpreting it.

The irreducibility of the special sciences creates no problem for the dualist, who sees the explanatory endeavor of the physical sciences as something carried on from a perspective conceptually outside of the physical world.

But psychology is one of the least likely of sciences to be reduced. If psychology cannot be reduced, this line of reasoning leads to real emergence for mental acts and hence to a real dualism for the properties those acts instantiate Robinson There is an argument, which has roots in Descartes Meditation VI , which is a modal argument for dualism. One might put it as follows:. The rationale of the argument is a move from imaginability to real possibility.

I include 2 because the notion of conceivability has one foot in the psychological camp, like imaginability, and one in the camp of pure logical possibility and therefore helps in the transition from one to the other. See, for example, Chalmers , 94—9. This latter argument, if sound, would show that conscious states were something over and above physical states.

It is a different argument because the hypothesis that the unaltered body could exist without the mind is not the same as the suggestion that the mind might continue to exist without the body, nor are they trivially equivalent. The zombie argument establishes only property dualism and a property dualist might think disembodied existence inconceivable — for example, if he thought the identity of a mind through time depended on its relation to a body e.

When philosophers generally believed in contingent identity, that move seemed to them invalid. But nowadays that inference is generally accepted and the issue concerns the relation between imaginability and possibility.

No-one would nowadays identify the two except, perhaps, for certain quasi-realists and anti-realists , but the view that imaginability is a solid test for possibility has been strongly defended. There seem to be good arguments that time-travel is incoherent, but every episode of Star-Trek or Doctor Who shows how one can imagine what it might be like were it possible.

It is worth relating the appeal to possibility in this argument to that involved in the more modest, anti-physicalist, zombie argument. The possibility of this hypothesis is also challenged, but all that is necessary for a zombie to be possible is that all and only the things that the physical sciences say about the body be true of such a creature. As the concepts involved in such sciences — e. There is no parallel clear, uncontroversial and regimented account of mental concepts as a whole that fails to invoke, explicitly or implicitly, physical e.

For an analytical behaviourist the appeal to imaginability made in the argument fails, not because imagination is not a reliable guide to possibility, but because we cannot imagine such a thing, as it is a priori impossible.

The impossibility of disembodiment is rather like that of time travel, because it is demonstrable a priori, though only by arguments that are controversial. The argument can only get under way for those philosophers who accept that the issue cannot be settled a priori, so the possibility of the disembodiment that we can imagine is still prima facie open. A major rationale of those who think that imagination is not a safe indication of possibility, even when such possibility is not eliminable a priori, is that we can imagine that a posteriori necessities might be false — for example, that Hesperus might not be identical to Phosphorus.

But if Kripke is correct, that is not a real possibility. Another way of putting this point is that there are many epistemic possibilities which are imaginable because they are epistemic possibilities, but which are not real possibilities. Richard Swinburne , New Appendix C , whilst accepting this argument in general, has interesting reasons for thinking that it cannot apply in the mind-body case.

In the case of our experience of ourselves this is not true. Now it is true that the essence of Hesperus cannot be discovered by a mere thought experiment. That is because what makes Hesperus Hesperus is not the stereotype, but what underlies it.

But it does not follow that no one can ever have access to the essence of a substance, but must always rely for identification on a fallible stereotype. One might think that for the person him or herself, while what makes that person that person underlies what is observable to others, it does not underlie what is experienceable by that person, but is given directly in their own self-awareness.

This is a very appealing Cartesian intuition: my identity as the thinking thing that I am is revealed to me in consciousness, it is not something beyond the veil of consciousness. Now it could be replied to this that though I do access myself as a conscious subject, so classifying myself is rather like considering myself qua cyclist.

Just as I might never have been a cyclist, I might never have been conscious, if things had gone wrong in my very early life. I am the organism, the animal, which might not have developed to the point of consciousness, and that essence as animal is not revealed to me just by introspection.

But there are vital differences between these cases. A cyclist is explicitly presented as a human being or creature of some other animal species cycling: there is no temptation to think of a cyclist as a basic kind of thing in its own right. Consciousness is not presented as a property of something, but as the subject itself. Yet, even if we are not referring primarily to a substrate, but to what is revealed in consciousness, could it not still be the case that there is a necessity stronger than causal connecting this consciousness to something physical?

To consider this further we must investigate what the limits are of the possible analogy between cases of the water-H 2 O kind, and the mind-body relation. We start from the analogy between the water stereotype — how water presents itself — and how consciousness is given first-personally to the subject. It is plausible to claim that something like water could exist without being H 2 O, but hardly that it could exist without some underlying nature.

There is, however, no reason to deny that this underlying nature could be homogenous with its manifest nature: that is, it would seem to be possible that there is a world in which the water-like stuff is an element, as the ancients thought, and is water-like all the way down.

The claim of the proponents of the dualist argument is that this latter kind of situation can be known to be true a priori in the case of the mind: that is, one can tell by introspection that it is not more-than-causally dependent on something of a radically different nature, such as a brain or body. What grounds might one have for thinking that one could tell that a priori? The only general argument that seem to be available for this would be the principle that, for any two levels of discourse, A and B , they are more-than-causally connected only if one entails the other a priori.

And the argument for accepting this principle would be that the relatively uncontroversial cases of a posteriori necessary connections are in fact cases in which one can argue a priori from facts about the microstructure to the manifest facts. In the case of water, for example, it would be claimed that it follows a priori that if there were something with the properties attributed to H 2 O by chemistry on a micro level, then that thing would possess waterish properties on a macro level.

What is established a posteriori is that it is in fact H 2 O that underlies and explains the waterish properties round here, not something else: the sufficiency of the base — were it to obtain — to explain the phenomena, can be deduced a priori from the supposed nature of the base. This is, in effect, the argument that Chalmers uses to defend the zombie hypothesis. The suggestion is that the whole category of a posteriori more-than-causally necessary connections often identified as a separate category of metaphysical necessity comes to no more than this.

If we accept that this is the correct account of a posteriori necessities, and also deny the analytically reductionist theories that would be necessary for a priori connections between mind and body, as conceived, for example, by the behaviourist or the functionalist, does it follow that we can tell a priori that consciousness is not more-than-causally dependent on the body?

Though we shall see later, in 5. The conceivability argument creates a prima facie case for thinking that mind has no more than causal ontological dependence on the body. Let us assume that one rejects analytical behaviourist or functionalist accounts of mental predicates.

Then the above arguments show that any necessary dependence of mind on body does not follow the model that applies in other scientific cases. This does not show that there may not be other reasons for believing in such dependence, for so many of the concepts in the area are still contested. For example, it might be argued that identity through time requires the kind of spatial existence that only body can give: or that the causal continuity required by a stream of consciousness cannot be a property of mere phenomena.

All these might be put forward as ways of filling out those aspects of our understanding of the self that are only obliquely, not transparently, presented in self-awareness. The dualist must respond to any claim as it arises: the conceivability argument does not pre-empt them. All the arguments so far in this section have been either arguments for property dualism only, or neutral between property and substance dualism.

In this subsection, and in section 4. The ones in this section can be regarded as preliminaries to that in 4. He famously expresses his theory as follows. Nevertheless, in the Appendix of the same work he expressed dissatisfaction with this account. Somewhat surprisingly, it is not very clear just what his worry was, but it is expressed as follows:. This Berkeleian view is expressed in more modern terms by John Foster. There is a clash of intuitions here between which it is difficult to arbitrate.

There is an argument that is meant to favour the need for a subject, as claimed by Berkeley and Foster. To say that, according to the bundle theory, the identity conditions of individual mental states must be independent of the identity of the person who possesses them, is to say that their identity is independent of the bundle to which they belong.

Perhaps the identity of a mental event is bound up with the complex to which it belongs. That this is impossible certainly needs further argument. Hume seems, however, in the main text to unconsciously make a concession to the opposing view, namely the view that there must be something more than the items in the bundle to make up a mind.

He says:. Talk of the mind as a theatre is, of course, normally associated with the Cartesian picture, and the invocation of any necessary medium, arena or even a field hypostasize some kind of entity which binds the different contents together and without which they would not be a single mind.

Modern Humeans — such as Parfit ; or Dainton — replace the theatre with a co-consciousness relation. So the bundle theorist is perhaps not as restricted as Hume thought. The bundle consists of the objects of awareness and the co-consciousness relation or relations that hold between them , and I think that the modern bundle theorist would want to say that it is the nexus of co-consciousness relations that constitutes our sense of the subject and of the act of awareness of the object.

The Humean point then becomes that we mistake the nexus of relations for a kind of entity, in a way similar to that in which, Hume claims,we mistake the regular succession of similar impressions for an entity called an enduring physical object. Whether this really makes sense in the end is another matter. I think that it is dubious whether it can accommodate the subject as agent , but it does mean that simple introspection probably cannot refute a sophisticated bundle theory in the way that Lowe and Foster want.

The rejection of bundle dualism, therefore, requires more than an appeal to our intuitive awareness of ourselves as subjects. We will see in the next section how arguments that defend the simplicity of the self attempt to undercut the bundle theory. There is a long tradition, dating at least from Reid , for arguing that the identity of persons over time is not a matter of convention or degree in the way that the identity of other complex substances is and that this shows that the self is a different kind of entity from any physical body.

Criticism of these arguments and of the intuitions on which they rest, running from Hume to Parfit , have left us with an inconclusive clash of intuitions. The argument under consideration and which, possibly, has its first statement in Madell , does not concern identity through time, but the consequences for identity of certain counterfactuals concerning origin. It can, perhaps, therefore, break the stalemate which faces the debate over diachronic identity.

The claim is that the broadly conventionalist ways which are used to deal with problem cases through time for both persons and material objects, and which can also be employed in cases of counterfactuals concerning origin for bodies, cannot be used for similar counterfactuals concerning persons or minds.

Concerning ordinary physical objects, it is easy to imagine counterfactual cases where questions of identity become problematic. Take the example of a particular table. We can scale counterfactual suggestions as follows:.

The first suggestion would normally be rejected as clearly false, but there will come a point along the spectrum illustrated by i and iii and towards iii where the question of whether the hypothesised table would be the same as the one that actually exists have no obvious answer. There will thus be a penumbra of counterfactual cases where the question of whether two things would be the same is not a matter of fact.

Four statements were included, each relating to an aspect of the mind-brain relationship. The Edinburgh survey revealed a predominance of dualistic attitudes emphasizing the separateness of mind and brain.

Religious belief was found to be the best predictor for dualistic attitudes. If minds are not differentiated by their contents and have no spatial positions to distinguish them, there remains no basis for individuating their identities. On numerically individuating non-physical substances, see Armstrong, , pp. For a general discussion of whether the self is a substance, see Shoemaker, , ch. After taking up his celebrated method of doubt, which commits him to reject as false anything that is in the slightest degree uncertain, Descartes finds that the entirety of the physical world is uncertain.

Perhaps, after all, it is nothing but an elaborate phantasm wrought by an all-powerful and infinitely clever, but deceitful, demon. Still, he cannot doubt his own existence, since he must exist to doubt. Because he thinks, he is. But he cannot be his body, since that identity is doubtful and possibly altogether false. In sum, I cannot doubt the existence of my mind, but I can doubt the existence of my body. From this I knew that I was a substance the whole essence or nature of which was merely to think, and which, in order to exist, needed no place and depended on no material things.

The Argument from Indubitability has been maligned in the philosophical literature from the very beginning. Perhaps it also belongs to my essence to be something extended. Suppose that I cannot doubt whether a given figure is a triangle, but can doubt whether its interior angles add up to two right angles. It does not follow from this that the number of degrees in triangles may be more or less than This is because the doubt concerning the number of degrees in a triangle is a property of me, not of triangles.

The dualist can reply in two ways. First, he or she may argue that, while doubting the body is not a property of bodies, being doubtable is a property of bodies. Second, the dualist may reply that it is always possible to doubt whether the figure before me is a triangle.

Consider, for example, the following parallel argument from Paul Churchland , p. Following Descartes, it ought to be that Ali is not Clay though in fact Clay was a famous heavyweight and identical to Ali. By way of reply, surely it is possible for an evil demon to deceive me about whether Mohammed Ali was a famous heavyweight boxer. So, the dualist might insist, the case of mind is unique in its immunity from doubt. It is only with reference to our own mental states that we can be said to know incorrigibly.

A third argument in the Meditations maintains that the mind and body must really be separate because Descartes can conceive of the one without the other.

Since he can clearly and distinctly understand the body without the mind and vice versa, God could really have created them separately. But if the mind and body can exist independently, they must really be independent, for nothing can constitute a part of the essence of a thing that can be absent without the thing itself ceasing to be. If the essence of the mind is incorporeal, so must be the mind itself. The general strategy is to identify some property or feature indisputably had by mental phenomena but not attributable in any meaningful way to bodily or nervous phenomena, or vice versa.

For example, some have suggested that mental states are private in the sense that only those who possess them can know them directly. The latter assumes a correlation, if not an identity, between nervous and mental states or events. My linguistic, bodily and neural activities are public in the sense that anyone suitably placed can observe them. Since mental states are private to their possessors, but brain states are not, mental states cannot be identical to brain states.

Rey pp. Others can know my mental states only by making inferences based on my verbal, non-verbal or neurophysiological activity. You may infer that I believe it will rain from the fact that I am carrying an umbrella, but I do not infer that I believe it will rain from noticing that I am carrying an umbrella.

I do not need to infer my mental states because I know them immediately. Since mental states are knowable without inference in the first person case, but are knowable or at least plausibly assigned only by inference in the third person case, we have an authority or incorrigibility with reference to our own mental states that no one else could have.

Since beliefs about the physical world are always subject to revision our inferences or theories could be mistaken , mental states are not physical states. Some mental states exhibit intentionality. Intentional mental states include, but are not limited to, intendings , such as plans to buy milk at the store. They are states that are about, of, for, or towards things other than themselves. Desires, beliefs, loves, hates, perceptions and memories are common intentional states.

For example, I may have a desire for an apple; I may have love for or towards my neighbor; I may have a belief about republicans or academics; or I may have memories of my grandfather. The dualist claims that brain states, however, cannot plausibly be ascribed intentionality. How can a pattern of neural firings be of or about or towards anything other than itself? As a purely physical event, an influx of sodium ions through the membrane of a neural cell creating a polarity differential between the inside and outside of the cell wall, and hence an electrical discharge, cannot be of Paris, about my grandfather, or for an apple.

No physical phenomena exhibits anything similar. Taylor, pp. My belief that it will rain can be either true or false. But, the dualist may urge, as a purely physical event, an electrical or chemical discharge in the brain cannot be true or false. Indeed, it lacks not only truth, but also linguistic meaning. Since mental states such as beliefs possess truth-value and semantics, it seems incoherent to attribute these properties to bodily states.

Thus, mental states are not bodily states. Presumably, then, the minds that have these states are also non-physical. Churchland, , p. Although each of these arguments for dualism may be criticized individually, they are typically thought to share a common flaw: they assume that because some aspect of mental states, such as privacy, intentionality, truth, or meaning cannot be attributed to physical substances, they must be attributable to non-physical substances.

But if we do not understand how such states and their properties can be generated by the central nervous system, we are no closer to understanding how they might be produced by minds.

Nagel, , p. Dualists cannot explain the mechanisms by which souls generate meaning, truth, intentionality or self-awareness. Thus, dualism creates no explanatory advantage. If the only reasons for supposing that non-physical minds exist are the phenomena of intentionality, privacy and the like, then dualism unnecessarily complicates the metaphysics of personhood. We can ask how much the brain weighs, but not how much the mind weighs. We can ask how many miles per hour my body is moving, but not how many miles per hour my mind is moving.

Minds are just not the sorts of things that can have size, shape, weight, location, motion, and the other attributes that Descartes ascribes to extended reality. We literally could not understand someone who informed us that the memories of his last holiday are two inches behind the bridge of his nose or that his perception of the color red is straight back from his left eye.

Another argument for dualism claims that dualism is required for free will. If dualism is false, then presumably materialism, the thesis that humans are entirely physical beings, is true. We set aside consideration of idealism —the thesis that only minds and ideas exist. If materialism were true, then every motion of bodies should be determined by the laws of physics, which govern the actions and reactions of everything in the universe.

But a robust sense of freedom presupposes that we are free, not merely to do as we please, but that we are free to do otherwise than as we do. This, in turn, requires that the cause of our actions not be fixed by natural laws. Since, according to the dualist, the mind is non-physical, there is no need to suppose it bound by the physical laws that govern the body.

So, a strong sense of free will is compatible with dualism but incompatible with materialism. Since freedom in just this sense is required for moral appraisal, the dualist can also argue that materialism, but not dualism, is incompatible with ethics. Taylor, , p. Rey, , pp. This, the dualist may claim, creates a strong presumption in favor of their metaphysics. This argument is sometimes countered by arguing that free will is actually compatible with materialism or that even if the dualistic account of the will is correct, it is irrelevant because no volition on the part of a non-physical substance could alter the course of nature anyway.

Man would be free only if there was nothing he could do. Property dualists are not committed to the existence of non-physical substances, but are committed to the irreducibility of mental phenomena to physical phenomena.

An argument for property dualism, derived from Thomas Nagel and Saul Kripke, is as follows: We can assert that warmth is identical to mean kinetic molecular energy, despite appearances, by claiming that warmth is how molecular energy is perceived or manifested in consciousness. Similarly, color is identical to electromagnetic reflectance efficiencies, inasmuch as color is how electromagnetic wavelengths are processed by human consciousness.

In these cases, the appearance can be distinguished from the reality. Heat is molecular motion, though it appears to us as warmth. Other beings, for example, Martians, might well apprehend molecular motion in another fashion. They would grasp the same objective reality, but by correlating it with different experiences. We move toward a more objective understanding of heat when we understand it as molecular energy rather than as warmth.

Consciousness itself, however, cannot be reduced to brain activity along analogous lines because we should then need to say that consciousness is how brain activity is perceived in consciousness, leaving consciousness unreduced. Put differently, when it comes to consciousness, the appearance is the reality. Therefore, no reduction is possible. Nagel writes:. The idea of moving from appearance to reality seems to make no sense here. What is the analogue in this case to pursuing a more objective understanding of the same phenomena by abandoning the initial subjective viewpoint toward them in favor of another that is more objective but concerns the same thing?

Certainly it appears unlikely that we will get closer to the real nature of human experience by leaving behind the particularity of our human point of view and striving for a description in terms accessible to beings that could not imagine what it was like to be us.

Nagel ; reprinted in Block et. Consciousness is thus sui generis of its own kind , and successful reductions elsewhere should give us little confidence when it comes to experience. Mentality is a broad and complex property. Some things—in particular, persons and certain biological organisms—can also instantiate mental properties, like being in pain and liking the taste of avocado. Once we admit the existence of mental properties, we can inquire into the nature of the relationship between mental and physical properties.

According to the supervenience thesis , there can be no mental differences without corresponding physical differences. If, for example, I feel a headache, there must be some change not only in my mental state, but also in my body presumably, in my brain. If Mary is in pain, but Erin is not, then, according to the supervenience thesis, there must be a physical difference between Mary and Erin.

Kim, p. Why deny supervenience? If it is possible to have mental differences without physical differences, then mental properties cannot be identical to or reducible to physical properties. They would exist as facts about the world over and above the purely physical facts. Kim, and following. Without the actual existence of such a world, the argument that mental properties do not supervene on physical properties fails.

A second rebuttal avers that absent qualia thought experiments and inverted spectra though experiments only support property dualism if we can imagine these possibilities obtaining.

We may think we can conceive of such a world but attempts to do so do not actually achieve such a conception. If it is, its truth is necessary. If, then, someone thought that they imagined a proof that the thesis is false, they would be conceiving the falsity of what is in reality a necessary truth.

This is implausible. But perhaps the physicalist can come up with independent reasons for supposing that the dualist has failed to imagine what she claims. The physicalist can point, for example, to successful reductions in other areas of science. On the basis of these cases she can argue the implausibility of supposing that, uniquely, mental phenomena resist reduction to the causal properties of matter. That is, an inductive argument for reduction outweighs a conceivability argument against reduction.

And in that case, the dualist must do more than merely insist that she has correctly imagined inverted spectra in isomorphic individuals. For useful discussions of some of these issues, see Tye and Horgan It is often alleged, more broadly, that dualism is unscientific and renders impossible any genuine science of mind or truly empirical psychology.

Those eager to defend the relevance of science to the study of mind, such as Paul Churchland, have argued that dualism is inconsistent with the facts of human evolution and fetal development. According to this view, we began as wholly physical beings. This is true of the species and the individual human. No one seriously supposes that newly fertilized ova are imbued with minds or that the original cell in the primordial sea was conscious.

But from those entirely physical origins, nothing non-physical was later added. We can explain the evolution from the unicellular stage to present complexities by means of random mutations and natural selection in the species case and through the accretion of matter through nutritional intake in the individual case.

But if we, as species or individuals, began as wholly physical beings and nothing nonphysical was later added, then we are still wholly physical creatures. Thus, dualism is false. The above arguments are only as strong as our reasons for thinking that we began as wholly material beings and that nothing non-physical was later added. Some people, particularly the religious, will object that macro-evolution of a species is problematic or that God might well have infused the developing fetus with a soul at some point in the developmental process traditionally at quickening.

Most contemporary philosophers of mind put little value in these rejoinders. Others argue that dualism is scientifically unacceptable because it violates the well-established principle of the conservation of energy.

Interactionists argue that mind and matter causally interact. But if the spiritual realm is continually impinging on the universe and effecting changes, the total level of energy in the cosmos must be increasing or at least fluctuating.

This is because it takes physical energy to do physical work. If the will alters states of affairs in the world such as the state of my brain , then mental energy is somehow converted into physical energy. At the point of conversion, one would anticipate a physically inexplicable increase in the energy present within the system.

First, they could deny the sacredness of the principle of the conservation of energy. This would be a desperate measure. The principle is too well established and its denial too ad hoc. Second, the dualist might offer that mind does contribute energy to our world, but that this addition is so slight, in relation to our means of detection, as to be negligible.