The Coherence of Theism
3
An Immaterial person
In everyday use the word “person" means “a human being.” But in what follows I will be using the word in a more specific way. It will refer to, “a conscious being that has rational thoughts, memories, moral awareness, intentions, continuity of identity and is able to perform various basic and nonbasic actions.” [1] Given this definition of a person, is the concept of an immaterial person logically incoherent in either sense sketched out in the Introduction?
Note first that the words immaterial and person do not stand in strict logical opposition in the way square and circle do. It is characteristic of cases of strict logical incoherence that the entities and states of affairs that they postulate are inconceivable. It is not possible to visualise a perfectly circular polygon with four equal sides or to rationally intuit what it means for a man to be simultaneously married and unmarried. But the concept of a disembodied person does not have this property of inconceivability. It is easy to imagine the experience of losing your body and retaining your mental life. Indeed, we do this whenever we read accounts by those who claim to have had out of body experiences. And it is also possible to imagine what it would mean if, so disembodied, we discovered we could move objects or perform other actions simply by forming the intention to do so.
So much for the strict logical incoherence of the concept of an immaterial person. But is it logically incoherent in the broad sense which I have defined? Whether you think so will depend on whether or not you are prepared to affirm a metaphysical worldview known as physicalism.
Physicalism, or materialism, is the theory that ultimate reality is reducible to physical particles and their movements and modifications. On this view, there can be no such things as Platonic objects, objective moral values or immaterial beings and substances. Consciousness, the physicalist claims, is either an epiphenomenon of physical brain states or else just is a physical process in the brain. Whichever view is adopted, it follows that mental states cannot possibly exist without the physical substrate of the brain and so for the physicalist the concept of an “immaterial person” is logically incoherent in the broad sense. If you hold that consciousness depends on the physical brain, then the proposition, An immaterial mind exists entails a contradiction. For if A mind exists entails A brain is functioning, then A brain is functioning obviously entails A brain exists. Thus, An immaterial mind exists entails A brain exists and does not exist at the same time and in the same respect--which is just to say, “P is Q and not-Q.” But is physicalism itself coherent?
1. Physicalism
Strictly speaking, inductive knowledge does not belong in an a priori objection. Inductive knowledge is based on observation and the phrase “a priori objection” means, “an objection prior to observation.” And while it may be true that every mind of which we have direct knowledge is embodied this does not prove that unembodied minds are logically impossible; indeed, inductive knowledge cannot prove that anything is logically impossible.
In the philosophy of science, this is called, “The problem of induction.” Consider: In inductive reasoning, one makes a series of observations and infers a conclusion. For instance, having observed many swans and found them all to be white, it seems valid to conclude, All swans are white. But no number of confirming observations, however large, can prove a universal generalisation—no number of white swans, however large, can preclude the possibility of encountering a black swan. Only deductive conclusions in mathematics and philosophy are logically necessary; conclusions based on observation, however reliable they seem, are always in principle falsifiable—a fact which led the philosopher C. D. Broad to declare that, “induction is the glory of science and the scandal of philosophy.”
But suppose that we take a hint from Wittgenstein who recommended a slight relaxation of the distinction between analytic and synthetic propositions. Wittgenstein, that is, stressed the importance of including very basic empirical propositions of the sort we are taught as children (such as that, “the Earth is round and men's heads are not full of sawdust and cars do not grow out of the ground") among our first principles. “Propositions of the form of empirical propositions," he writes, “and not only propositions of logic, form the foundation of all operating with thoughts.” On this view, might the fact that every mind observed is embodied count against the logical coherence of the concept of an immaterial mind?
I will admit that I had some initial sympathy with physicalistic accounts of the mind. The inference from all known examples of minds as embodied to the idea that minds and bodies are indissociable seems plausible. And the observation that our bodily states (such as drunkenness and fatigue) affect our mental states seems to support it. However, even if we admit inductive knowledge into the discussion, the objection to the concept of an immaterial mind does not obtain. And this is because physicalism (as we shall we) cannot by itself account for our mental states. Consider, by way of analogy, a scientist who claims that a certain bacteria cannot survive at low temperatures because it has only ever been observed at high temperatures. If it is later proven that the bacteria in question cannot reproduce at high temperatures, then clearly the argument has lost all force. To tell the complete story of that bacteria, we will need to understand it in a way that includes its independence from high-temperature environments.
2. Arguments Against Physicalism
This is a subject that will be discussed in detail in my Chapter on the Argument from Consciousness. For now I will just provide a very brief sketch of three forceful arguments from the literature to establish my preliminary claim that it is impossible to give a complete account of the mind using only the explanatory resources of physicalism. [2]
2.1 Mental States Are Irreducible
Reduction in the physical sciences, notes Swinburne, is achieved by distinguishing mental phenomena from more fundamental physical phenomena and giving primacy to the latter. Warmth, for instance, is reduced to molecular energy in thermodynamics. Thereafter, molecular energy is understood to be what warmth, “really is.” Because sensory perception is subjective and can show variation between individuals and species, we move toward a more objective knowledge of the world when we understand it in this way: when we understand warmth as the way in which molecular energy is perceived in consciousness; or understand colour as the way in which electromagnetic wavelengths are perceived in consciousness—and so on. “What the evidence of the history of science shows,” continues Swinburne, “is that the way to achieve integration of sciences is to ignore the mental.” But an intractable problem arises when we come to the mental itself: We do not move towards a more objective understanding of consciousness when we attempt to understand consciousness as the way in which brain activity is perceived in consciousness: It is incoherent to reduce consciousness to some more fundamental physical phenomenon and ignore the former because the former, consciousness, is the very thing we are attempting to explain.
2.2 The Intentionality of Mental States
A second property of mental states that physicalism cannot account for is what philosophers call their intentionality. By this they simply mean that thoughts are always about or of something external to themselves. When you think about shoes and ships and sealing-wax, your thoughts are in those moments of or about shoes and ships and sealing-wax.
The intractable problem intentionality raises for physicalism can be drawn out in the following way.
Consider the word moon penciled on a piece of paper. In the absence of a literate observer to read the word and associate it with the moon, can the carbon particles of pencil lead and the wood pulp that composes the sheet of paper be said to be “about” the moon? Clearly not. And what can be said of a printed word on the page can be said equally of physical brain states. A pattern of firing neurones representing someone's thought about the moon cannot, in the absence of a conscious observer to experience that brain event as a thought about the moon, be said to be “neurones about the moon” in any meaningful and objective sense. Physical things (whether they be neurones or particles of pencil lead or teapots or rocks) are not representational in the way that mental states are. And so an exhaustive physicalistic description of mental states would leave something essential to them out of account.
And nor, interestingly, can the physicalist simply deny the existence of intentionality. This is because the thought, “Thoughts do not have intentionality,” must itself be about intentionality in order to pick out and deny intentionality—and must therefore have intentionality. The denial of intentionality suffers from what Plantinga has called, “self-referential inconsistency.” It cannot be rationally affirmed.
2.3 Privileged Access of Mental States
But the most essential property of mental states which physicalism cannot account for is their personal immediacy to the subject who experiences them. “A mental property,” as Swinburne puts it, “is one to whose instantiation the substance in which it is instantiated necessarily has privileged access.” To help us understand this problem, Swinburne invites us to consider the following thought experiment. It is a helpful preliminary to what follows to note that people can enjoy a relatively normal mental life with only half a brain—after a procedure known as an “anatomical hemispherectomy.”
Suppose, firstly, that Swinburne is involved in a car accident that destroys his body but leaves his brain intact; suppose, secondly, that this occurs at a future date when brain transplants are feasible; suppose, finally, that a whimsical surgeon is responsible for the treatment of Swinburne and decides to perform a bizarre experiment: He will transplant the left hemisphere of Swinburne's brain in one donor body and the right hemisphere of his brain into another donor body. Let us refer to these two new bodies, each of which contains one half of Swinburne's brain, as Person A and Person B. The operation is a success. Person A and Person B recover and both somewhat resemble Swinburne in terms of character and memory. The question arises whether Swinburne has survived the operation. The claim that Swinburne is now both Person A and Person B is eliminable by a law of logic known as the identity of indiscernibles. Very simply expressed: If Swinburne is identical to Person A and Person B, then Person A and Person B are identical to each other and are therefore the same person—which they are not. [4] The remaining possibilities are that Swinburne is Person A or that he is Person B or that he is neither because the operation destroyed him.
The relevance of this thought experiment to physicalism is as follows. Whether or not Swinburne survived the bizarre experiment is an objective fact about the world. But it will not be possible to know the answer by either the most thorough cross-examination of Person A and Person B or the most exhaustive physicalistic description of their respective hemispheres. And so an exhaustive physicalistic description of the universe would leave something essential out of account; namely, who experienced which brain states.
What arguments of this sort bring out is the “privileged access" of the subject to his own mental life—what Searle calls their, “first person ontology.” “Others,” Swinburne writes, “can learn about my pains and thoughts by studying my behaviour and perhaps also by studying my brain. Yet I, too, could study my behaviour (I could watch a film of myself; I could study my brain via a system of mirrors and microscopes) just as well as anyone else could. But I have a way of knowing about pains and thoughts other than those available to the best student of my behaviour or brain: I experience them.” The problem this raises for physicalism is that what makes a mental event a mental event is not the public knowledge captured by physicalism but precisely this private knowledge that physicalism cannot capture.
2.4 The Conceivability Argument
I mentioned at the start of his chapter that immaterial minds are not inconceivable—whether or not they exist, we can at least conceive of them existing. From this fact some philosophers of mind have extrapolated a forceful argument for substance dualism—the position that the mind and body are indeed two separate things or “substances.” In what follows, I will be summarising the discussion provided by Edward Feser in Philosophy of Mind: A Beginner’s Guide. The argument begins with a few preliminary precepts.
Feser first introduces a distinction between two kinds of impossibility: physical impossibility and metaphysical impossibility. It is helpful here to think of this as a distinction between strong and weak forms of impossibility. A state of affairs is merely physically impossible if, though impossible in the actual world, we can give a description of it obtaining in some hypothetical world without contradiction. In this connection, consider the proposition,
Note first that the words immaterial and person do not stand in strict logical opposition in the way square and circle do. It is characteristic of cases of strict logical incoherence that the entities and states of affairs that they postulate are inconceivable. It is not possible to visualise a perfectly circular polygon with four equal sides or to rationally intuit what it means for a man to be simultaneously married and unmarried. But the concept of a disembodied person does not have this property of inconceivability. It is easy to imagine the experience of losing your body and retaining your mental life. Indeed, we do this whenever we read accounts by those who claim to have had out of body experiences. And it is also possible to imagine what it would mean if, so disembodied, we discovered we could move objects or perform other actions simply by forming the intention to do so.
So much for the strict logical incoherence of the concept of an immaterial person. But is it logically incoherent in the broad sense which I have defined? Whether you think so will depend on whether or not you are prepared to affirm a metaphysical worldview known as physicalism.
Physicalism, or materialism, is the theory that ultimate reality is reducible to physical particles and their movements and modifications. On this view, there can be no such things as Platonic objects, objective moral values or immaterial beings and substances. Consciousness, the physicalist claims, is either an epiphenomenon of physical brain states or else just is a physical process in the brain. Whichever view is adopted, it follows that mental states cannot possibly exist without the physical substrate of the brain and so for the physicalist the concept of an “immaterial person” is logically incoherent in the broad sense. If you hold that consciousness depends on the physical brain, then the proposition, An immaterial mind exists entails a contradiction. For if A mind exists entails A brain is functioning, then A brain is functioning obviously entails A brain exists. Thus, An immaterial mind exists entails A brain exists and does not exist at the same time and in the same respect--which is just to say, “P is Q and not-Q.” But is physicalism itself coherent?
1. Physicalism
Strictly speaking, inductive knowledge does not belong in an a priori objection. Inductive knowledge is based on observation and the phrase “a priori objection” means, “an objection prior to observation.” And while it may be true that every mind of which we have direct knowledge is embodied this does not prove that unembodied minds are logically impossible; indeed, inductive knowledge cannot prove that anything is logically impossible.
In the philosophy of science, this is called, “The problem of induction.” Consider: In inductive reasoning, one makes a series of observations and infers a conclusion. For instance, having observed many swans and found them all to be white, it seems valid to conclude, All swans are white. But no number of confirming observations, however large, can prove a universal generalisation—no number of white swans, however large, can preclude the possibility of encountering a black swan. Only deductive conclusions in mathematics and philosophy are logically necessary; conclusions based on observation, however reliable they seem, are always in principle falsifiable—a fact which led the philosopher C. D. Broad to declare that, “induction is the glory of science and the scandal of philosophy.”
But suppose that we take a hint from Wittgenstein who recommended a slight relaxation of the distinction between analytic and synthetic propositions. Wittgenstein, that is, stressed the importance of including very basic empirical propositions of the sort we are taught as children (such as that, “the Earth is round and men's heads are not full of sawdust and cars do not grow out of the ground") among our first principles. “Propositions of the form of empirical propositions," he writes, “and not only propositions of logic, form the foundation of all operating with thoughts.” On this view, might the fact that every mind observed is embodied count against the logical coherence of the concept of an immaterial mind?
I will admit that I had some initial sympathy with physicalistic accounts of the mind. The inference from all known examples of minds as embodied to the idea that minds and bodies are indissociable seems plausible. And the observation that our bodily states (such as drunkenness and fatigue) affect our mental states seems to support it. However, even if we admit inductive knowledge into the discussion, the objection to the concept of an immaterial mind does not obtain. And this is because physicalism (as we shall we) cannot by itself account for our mental states. Consider, by way of analogy, a scientist who claims that a certain bacteria cannot survive at low temperatures because it has only ever been observed at high temperatures. If it is later proven that the bacteria in question cannot reproduce at high temperatures, then clearly the argument has lost all force. To tell the complete story of that bacteria, we will need to understand it in a way that includes its independence from high-temperature environments.
2. Arguments Against Physicalism
This is a subject that will be discussed in detail in my Chapter on the Argument from Consciousness. For now I will just provide a very brief sketch of three forceful arguments from the literature to establish my preliminary claim that it is impossible to give a complete account of the mind using only the explanatory resources of physicalism. [2]
2.1 Mental States Are Irreducible
Reduction in the physical sciences, notes Swinburne, is achieved by distinguishing mental phenomena from more fundamental physical phenomena and giving primacy to the latter. Warmth, for instance, is reduced to molecular energy in thermodynamics. Thereafter, molecular energy is understood to be what warmth, “really is.” Because sensory perception is subjective and can show variation between individuals and species, we move toward a more objective knowledge of the world when we understand it in this way: when we understand warmth as the way in which molecular energy is perceived in consciousness; or understand colour as the way in which electromagnetic wavelengths are perceived in consciousness—and so on. “What the evidence of the history of science shows,” continues Swinburne, “is that the way to achieve integration of sciences is to ignore the mental.” But an intractable problem arises when we come to the mental itself: We do not move towards a more objective understanding of consciousness when we attempt to understand consciousness as the way in which brain activity is perceived in consciousness: It is incoherent to reduce consciousness to some more fundamental physical phenomenon and ignore the former because the former, consciousness, is the very thing we are attempting to explain.
2.2 The Intentionality of Mental States
A second property of mental states that physicalism cannot account for is what philosophers call their intentionality. By this they simply mean that thoughts are always about or of something external to themselves. When you think about shoes and ships and sealing-wax, your thoughts are in those moments of or about shoes and ships and sealing-wax.
The intractable problem intentionality raises for physicalism can be drawn out in the following way.
Consider the word moon penciled on a piece of paper. In the absence of a literate observer to read the word and associate it with the moon, can the carbon particles of pencil lead and the wood pulp that composes the sheet of paper be said to be “about” the moon? Clearly not. And what can be said of a printed word on the page can be said equally of physical brain states. A pattern of firing neurones representing someone's thought about the moon cannot, in the absence of a conscious observer to experience that brain event as a thought about the moon, be said to be “neurones about the moon” in any meaningful and objective sense. Physical things (whether they be neurones or particles of pencil lead or teapots or rocks) are not representational in the way that mental states are. And so an exhaustive physicalistic description of mental states would leave something essential to them out of account.
And nor, interestingly, can the physicalist simply deny the existence of intentionality. This is because the thought, “Thoughts do not have intentionality,” must itself be about intentionality in order to pick out and deny intentionality—and must therefore have intentionality. The denial of intentionality suffers from what Plantinga has called, “self-referential inconsistency.” It cannot be rationally affirmed.
2.3 Privileged Access of Mental States
But the most essential property of mental states which physicalism cannot account for is their personal immediacy to the subject who experiences them. “A mental property,” as Swinburne puts it, “is one to whose instantiation the substance in which it is instantiated necessarily has privileged access.” To help us understand this problem, Swinburne invites us to consider the following thought experiment. It is a helpful preliminary to what follows to note that people can enjoy a relatively normal mental life with only half a brain—after a procedure known as an “anatomical hemispherectomy.”
Suppose, firstly, that Swinburne is involved in a car accident that destroys his body but leaves his brain intact; suppose, secondly, that this occurs at a future date when brain transplants are feasible; suppose, finally, that a whimsical surgeon is responsible for the treatment of Swinburne and decides to perform a bizarre experiment: He will transplant the left hemisphere of Swinburne's brain in one donor body and the right hemisphere of his brain into another donor body. Let us refer to these two new bodies, each of which contains one half of Swinburne's brain, as Person A and Person B. The operation is a success. Person A and Person B recover and both somewhat resemble Swinburne in terms of character and memory. The question arises whether Swinburne has survived the operation. The claim that Swinburne is now both Person A and Person B is eliminable by a law of logic known as the identity of indiscernibles. Very simply expressed: If Swinburne is identical to Person A and Person B, then Person A and Person B are identical to each other and are therefore the same person—which they are not. [4] The remaining possibilities are that Swinburne is Person A or that he is Person B or that he is neither because the operation destroyed him.
The relevance of this thought experiment to physicalism is as follows. Whether or not Swinburne survived the bizarre experiment is an objective fact about the world. But it will not be possible to know the answer by either the most thorough cross-examination of Person A and Person B or the most exhaustive physicalistic description of their respective hemispheres. And so an exhaustive physicalistic description of the universe would leave something essential out of account; namely, who experienced which brain states.
What arguments of this sort bring out is the “privileged access" of the subject to his own mental life—what Searle calls their, “first person ontology.” “Others,” Swinburne writes, “can learn about my pains and thoughts by studying my behaviour and perhaps also by studying my brain. Yet I, too, could study my behaviour (I could watch a film of myself; I could study my brain via a system of mirrors and microscopes) just as well as anyone else could. But I have a way of knowing about pains and thoughts other than those available to the best student of my behaviour or brain: I experience them.” The problem this raises for physicalism is that what makes a mental event a mental event is not the public knowledge captured by physicalism but precisely this private knowledge that physicalism cannot capture.
2.4 The Conceivability Argument
I mentioned at the start of his chapter that immaterial minds are not inconceivable—whether or not they exist, we can at least conceive of them existing. From this fact some philosophers of mind have extrapolated a forceful argument for substance dualism—the position that the mind and body are indeed two separate things or “substances.” In what follows, I will be summarising the discussion provided by Edward Feser in Philosophy of Mind: A Beginner’s Guide. The argument begins with a few preliminary precepts.
Feser first introduces a distinction between two kinds of impossibility: physical impossibility and metaphysical impossibility. It is helpful here to think of this as a distinction between strong and weak forms of impossibility. A state of affairs is merely physically impossible if, though impossible in the actual world, we can give a description of it obtaining in some hypothetical world without contradiction. In this connection, consider the proposition,
A man survived a headlong fall from the top of the Empire State Building.
This proposition is merely physically impossible because we can describe a possible world (say, one with very weak gravity) in which such a thing is possible. By contrast, a state of affairs is metaphysically impossible if it is impossible in the actual world and we cannot give a description of it obtaining in a possible world without contradiction. In this connection consider the proposition,
A married bachelor drafted a square circle.
This proposition is metaphysically impossible because we cannot coherently describe any possible world in which such a thing occurs. From this distinction we can derive a terse precept: Conceivability entails metaphysical possibility.
Let us now use this distinction to articulate a principle of identity: A is identical to B if and only if it is metaphysically impossible for A to exist apart from B; that is, only if we cannot conceive of any possible world in which A exists apart from B. Consider the claim that water is identical to H2O. If you can conceive of a possible world in which you have water without H2O, or H2O without water, then, sensu stricto, water and H2O are not identical but different substances.
Let us finally apply this principle of identity to the mind and body. If one can conceive of a possible world in which you have a mind without a body, then mind and body are not identical. And indeed one can conceive of such a possible world. W. D. Hart, for instance, invites us to imagine a man who wakes up one day and shuffles sleepily into the bathroom to wash his face. Looking in the mirror, he sees two empty sockets where his eyes should be. With a hacksaw, he then removes the top of his head and discovers that he has no brain. He saws off his entire head, his neck, his torso. At last his body is completely disposed of and he sees nothing in the mirror but the wall behind him. Of course, all of this is physically impossible but it also conceivable and therefore metaphysically possible.
W. D. Hart’s example is rather ghoulish but there are many other ways to conceive of mind and body existing apart from one another. Berkeleian idealism is one. Out of body experiences another. All of them are eminently conceivable. And from each of them it follows, ex hypothesi, that mind and body are not identical.
Against this, some opponents of substance dualism have argued that it is possible to conceive of two identical substances existing separately. For example: Water is identical to H2O. But now let there be a substance having the properties of liquidity, quenching thirst, freezing at low temperatures, etc. whose chemical composition is XYZ. If this is conceivable, then it is metaphysically possible; and if it is metaphysically possible, then A and B can be identical and conceived to exist separately and so the operating precept is violated.
However, Kripke, the American logician, fussily dispatches this objection. Let water be that substance which in every possible world has those properties which water has in the actual world; i.e., liquidity, quenching thirst, freezing at low temperatures, etc. Let H2O, meanwhile, be that substance which in every possible world has that chemical composition which H2O has in the actual world. Trivially, the substance in the actual world having the properties of water is the same substance in the actual world having the chemical composition H2O. But since “water” in every possible world is the same substance having the properties of water in the actual world, and the substance having the properties of water in the actual world is H2O, so the substance having those properties in every possible world is H2O. And so water and H2O are identical in every possible world.
In other words: To conceive of a substance similar to water that is not H2O is not to conceive of water existing apart from H2O but simply to conceive of a substance similar to water that is not water. The case of water and H2O does not therefore offer a counterexample to the test for metaphysical identicality. And so, we may conclude, the Conceivability Argument for Substance Dualism obtains.
As a final point it is worth noting that nonconceivability does not necessarily entail metaphysical impossibility: It does not follow from the fact that we cannot conceive of A existing apart from B that A and B are metaphysically identical. Maybe we just aren’t creative enough or intelligent enough to conceive of how it is possible for them to exist separately. But conceivability of separateness does entail metaphysical nonidenticality—which simple precept does all the work of the argument.
3. Mind is Essentially Nonphysical
It is vital to note that all of the problems under discussion are intractable to the physical sciences. Firstly, there is in principle no physical evidence which can circumvent the irreducibility of consciousness because the very structure of the reductive step, "Consciousness is the way in which p is experienced in consciousness," leaves consciousness unreduced no matter what physical evidence is substituted for p. Secondly, we can no more expect physical evidence to explain the intentionality of thought than we can expect an exhaustive chemical analysis of the carbon particles of pencil lead to eventually yield the meaning of the word moon which to a literate English observer they represent. Thirdly, physical evidence is by definition public and so can never collapse into or capture the privileged access of the subject to his own mental life which is, moreover, its essential feature. And, finally, the Conceivability Argument for Substance Dualism is an a priori argument on which the evidence of the physical sciences can have no bearing.
From here we can proceed by a disjunctive syllogism to the conclusion that mind is essentially nonphysical. [5]
Let us now use this distinction to articulate a principle of identity: A is identical to B if and only if it is metaphysically impossible for A to exist apart from B; that is, only if we cannot conceive of any possible world in which A exists apart from B. Consider the claim that water is identical to H2O. If you can conceive of a possible world in which you have water without H2O, or H2O without water, then, sensu stricto, water and H2O are not identical but different substances.
Let us finally apply this principle of identity to the mind and body. If one can conceive of a possible world in which you have a mind without a body, then mind and body are not identical. And indeed one can conceive of such a possible world. W. D. Hart, for instance, invites us to imagine a man who wakes up one day and shuffles sleepily into the bathroom to wash his face. Looking in the mirror, he sees two empty sockets where his eyes should be. With a hacksaw, he then removes the top of his head and discovers that he has no brain. He saws off his entire head, his neck, his torso. At last his body is completely disposed of and he sees nothing in the mirror but the wall behind him. Of course, all of this is physically impossible but it also conceivable and therefore metaphysically possible.
W. D. Hart’s example is rather ghoulish but there are many other ways to conceive of mind and body existing apart from one another. Berkeleian idealism is one. Out of body experiences another. All of them are eminently conceivable. And from each of them it follows, ex hypothesi, that mind and body are not identical.
Against this, some opponents of substance dualism have argued that it is possible to conceive of two identical substances existing separately. For example: Water is identical to H2O. But now let there be a substance having the properties of liquidity, quenching thirst, freezing at low temperatures, etc. whose chemical composition is XYZ. If this is conceivable, then it is metaphysically possible; and if it is metaphysically possible, then A and B can be identical and conceived to exist separately and so the operating precept is violated.
However, Kripke, the American logician, fussily dispatches this objection. Let water be that substance which in every possible world has those properties which water has in the actual world; i.e., liquidity, quenching thirst, freezing at low temperatures, etc. Let H2O, meanwhile, be that substance which in every possible world has that chemical composition which H2O has in the actual world. Trivially, the substance in the actual world having the properties of water is the same substance in the actual world having the chemical composition H2O. But since “water” in every possible world is the same substance having the properties of water in the actual world, and the substance having the properties of water in the actual world is H2O, so the substance having those properties in every possible world is H2O. And so water and H2O are identical in every possible world.
In other words: To conceive of a substance similar to water that is not H2O is not to conceive of water existing apart from H2O but simply to conceive of a substance similar to water that is not water. The case of water and H2O does not therefore offer a counterexample to the test for metaphysical identicality. And so, we may conclude, the Conceivability Argument for Substance Dualism obtains.
As a final point it is worth noting that nonconceivability does not necessarily entail metaphysical impossibility: It does not follow from the fact that we cannot conceive of A existing apart from B that A and B are metaphysically identical. Maybe we just aren’t creative enough or intelligent enough to conceive of how it is possible for them to exist separately. But conceivability of separateness does entail metaphysical nonidenticality—which simple precept does all the work of the argument.
3. Mind is Essentially Nonphysical
It is vital to note that all of the problems under discussion are intractable to the physical sciences. Firstly, there is in principle no physical evidence which can circumvent the irreducibility of consciousness because the very structure of the reductive step, "Consciousness is the way in which p is experienced in consciousness," leaves consciousness unreduced no matter what physical evidence is substituted for p. Secondly, we can no more expect physical evidence to explain the intentionality of thought than we can expect an exhaustive chemical analysis of the carbon particles of pencil lead to eventually yield the meaning of the word moon which to a literate English observer they represent. Thirdly, physical evidence is by definition public and so can never collapse into or capture the privileged access of the subject to his own mental life which is, moreover, its essential feature. And, finally, the Conceivability Argument for Substance Dualism is an a priori argument on which the evidence of the physical sciences can have no bearing.
From here we can proceed by a disjunctive syllogism to the conclusion that mind is essentially nonphysical. [5]
P1. Mind is either physical or nonphysical.
P2. It is not physical. C. Therefore, it is nonphysical. |
The logical structure of the argument is watertight. To avoid the conclusion, the physicalist needs to falsify one of the premises: Either by combing up with a new metaphysical category that is neither physical nor nonphysical or by demonstrating that mental states can be reduced to the physical. However, both of these escape routes are impassable in principle. The latter for reasons already discussed and the former because the notion of a metaphysical category neither physical nor nonphysical is as incoherent as an entity that has zero mass and has mass n or a colour that is neither primary red nor not primary red.
I began by noting that the concept of an immaterial person is incoherent on a physicalistic account of the mind. If a mind "just is" a physical brain state then of course the one cannot exist without the other. However, we have seen that physicalism entails the mind is reducible to the physical; that this cannot possibly be true; and that, therefore, its antithesis cannot possibly be false. The mind is irreducibly nonphysical. And, of course, the falsity of physicalism leaves the skeptic without grounds for rejecting the concept of an immaterial person.
I began by noting that the concept of an immaterial person is incoherent on a physicalistic account of the mind. If a mind "just is" a physical brain state then of course the one cannot exist without the other. However, we have seen that physicalism entails the mind is reducible to the physical; that this cannot possibly be true; and that, therefore, its antithesis cannot possibly be false. The mind is irreducibly nonphysical. And, of course, the falsity of physicalism leaves the skeptic without grounds for rejecting the concept of an immaterial person.
4. The Lack of Identifying Criteria
Some recent writers, while conceding that we can make sense of the concept of an immaterial person in all the above ways, have questioned whether it would ever be possible to identify and re-identify them; that is, whether there could ever be reliable criteria for differentiating between two different immaterial persons or even between one immaterial person encountered at two different times. The objection is not that immaterial persons are logically impossible but that if they did exist it would be logically impossible to identify them.
Even so, this objection depends upon a physicalistic understanding of personal identity in terms of bodily continuity. Allowing that it is not logically impossible that there exist immaterial persons (where a "person" is a conscious entity that has rational thoughts, memories, moral awareness, intentions, continuity of identity and who is able to perform basic and nonbasic actions) it is not logically impossible that such persons could provide proof of memory and character by performing basic actions and so successfully identify themselves. Such basic actions might include moving a planchette across a Ouija board during a séance, causing a specific pattern of vibrations in the air to produce a recognisable voice, or exciting a pattern of photons that together produce a recognisable image—all things of a sort spirits have been supposed to do.
5. Conclusion
We have seen that it is not incoherent in the strict sense to suppose that immaterial persons exist; and we have seen that the claim that it is logically incoherent in the broad sense depends on a commitment to a physicalistic worldview that cannot possibly account for our mental life. That we have a mental life of thoughts and perceptions is the most fundamental feature of human experience and the starting point for every other field of inquiry. It follows that any worldview that fails to account for our mental life cannot be rationally affirmed. And so any claim about that mental life which depends on physicalism cannot be rationally affirmed either. It is therefore not logically incoherent in either the strict or the broad sense to suppose that immaterial persons exist and nor is there any incoherence in supposing that such persons, if they exist, would be able to identify themselves.
However, the proposition that God exists is not simply the proposition that an immaterial person exists. God is also said to be omnipotent, omniscient, omnipresent, necessary, eternal and perfectly good. In the next chapter, I will consider whether an immaterial person with these divine attributes is a logically coherent concept.
Some recent writers, while conceding that we can make sense of the concept of an immaterial person in all the above ways, have questioned whether it would ever be possible to identify and re-identify them; that is, whether there could ever be reliable criteria for differentiating between two different immaterial persons or even between one immaterial person encountered at two different times. The objection is not that immaterial persons are logically impossible but that if they did exist it would be logically impossible to identify them.
Even so, this objection depends upon a physicalistic understanding of personal identity in terms of bodily continuity. Allowing that it is not logically impossible that there exist immaterial persons (where a "person" is a conscious entity that has rational thoughts, memories, moral awareness, intentions, continuity of identity and who is able to perform basic and nonbasic actions) it is not logically impossible that such persons could provide proof of memory and character by performing basic actions and so successfully identify themselves. Such basic actions might include moving a planchette across a Ouija board during a séance, causing a specific pattern of vibrations in the air to produce a recognisable voice, or exciting a pattern of photons that together produce a recognisable image—all things of a sort spirits have been supposed to do.
5. Conclusion
We have seen that it is not incoherent in the strict sense to suppose that immaterial persons exist; and we have seen that the claim that it is logically incoherent in the broad sense depends on a commitment to a physicalistic worldview that cannot possibly account for our mental life. That we have a mental life of thoughts and perceptions is the most fundamental feature of human experience and the starting point for every other field of inquiry. It follows that any worldview that fails to account for our mental life cannot be rationally affirmed. And so any claim about that mental life which depends on physicalism cannot be rationally affirmed either. It is therefore not logically incoherent in either the strict or the broad sense to suppose that immaterial persons exist and nor is there any incoherence in supposing that such persons, if they exist, would be able to identify themselves.
However, the proposition that God exists is not simply the proposition that an immaterial person exists. God is also said to be omnipotent, omniscient, omnipresent, necessary, eternal and perfectly good. In the next chapter, I will consider whether an immaterial person with these divine attributes is a logically coherent concept.
Footnotes
[1] Basic actions are actions, such as moving one’s hand, that are produced directly by the intention to perform them and do not depend on intermediary actions. Nonbasic actions are actions, such as posting a letter, that are produced by a sequence of intermediary basic actions—opening the front door, walking to the post office, and so on.
[2] For a more detailed discussion see Mind and Cosmos: Why the Materialist Neo-Darwinian Conception of Nature is Almost Certainly False by Thomas Nagel and Chapter 9 of The Existence of God and Chapter 7 of The Coherence of Theism by Richard Swinburne.
[3] The Identity of Indiscernibles, also knows as "Leibniz's Law" after its formulator Wilhelm Gottfried Leibniz, is a principle of analytic ontology which states that no two separate entities can have all their properties in common. The fact that Person A and Person B are physically distinct should not mislead us. Swinburne is concerned not with the body and brain per se but with the integrated personal identity and mental life of preoperative Swinburne—whether this is transplanted into either or neither of the postoperative bodies. It is true by tautology that the integrated “I” essential to personhood is not preserved when it is divided or doubly instantiated.
[4] A disjunctive syllogism is a rule of inference having the form, A or B. Not A. Therefore, B. Its validity depends on there being only two possible explanatory options. Thus, Either John is in Tokyo or he is not in Tokyo is a valid first premise because there is no third alternative; however, Either John is in Tokyo or he is in Osaka may not be a valid premise because it is possible that John is in Seoul or Beijing.
[1] Basic actions are actions, such as moving one’s hand, that are produced directly by the intention to perform them and do not depend on intermediary actions. Nonbasic actions are actions, such as posting a letter, that are produced by a sequence of intermediary basic actions—opening the front door, walking to the post office, and so on.
[2] For a more detailed discussion see Mind and Cosmos: Why the Materialist Neo-Darwinian Conception of Nature is Almost Certainly False by Thomas Nagel and Chapter 9 of The Existence of God and Chapter 7 of The Coherence of Theism by Richard Swinburne.
[3] The Identity of Indiscernibles, also knows as "Leibniz's Law" after its formulator Wilhelm Gottfried Leibniz, is a principle of analytic ontology which states that no two separate entities can have all their properties in common. The fact that Person A and Person B are physically distinct should not mislead us. Swinburne is concerned not with the body and brain per se but with the integrated personal identity and mental life of preoperative Swinburne—whether this is transplanted into either or neither of the postoperative bodies. It is true by tautology that the integrated “I” essential to personhood is not preserved when it is divided or doubly instantiated.
[4] A disjunctive syllogism is a rule of inference having the form, A or B. Not A. Therefore, B. Its validity depends on there being only two possible explanatory options. Thus, Either John is in Tokyo or he is not in Tokyo is a valid first premise because there is no third alternative; however, Either John is in Tokyo or he is in Osaka may not be a valid premise because it is possible that John is in Seoul or Beijing.