132. An Argument for Substance Dualism

I have been thinking a lot about what philosophical positions might be implied by the fact that we present and evaluate arguments. Consider this argument or set of premises from which a conclusion is derived:

Premise 1: All humans are mortal.

Premise 2: Socrates is a human.

Conclusion: So Socrates is mortal.

The English sentences in this argument express what the philosophical community typically refers to as propositions. In this post I want to explore how arguing might commit us to a certain view of propositions which, in turn, might commit us to some form of substance dualism that maintains the mind is a non-physical, simple (not made of parts), and non-spatial substance whereas the body is a physical, complex (made of parts), and spatial substance.

Let me begin my justification of this claim by asking: what are propositions? There are many controversial answers to this question. But one plausible view starts by recognizing that they are intentional or about something. And this “aboutness” makes them the proper bearers of true and falsity insofar as truth claims are obviously about things. For example, the sentence ‘Dwight Goodyear turned 47 years old in 2017’ expresses in English a proposition which is about me and can therefore be true or false (since I did indeed turn 47 in 2017 the proposition being expressed is true). If propositions weren’t about anything it is hard to see how they could be true or false.

Now intentionality is, to use a helpful definition from the Stanford Encyclopedia of Philosophy, “the power of minds to be about, to represent, or to stand for, things, properties and states of affairs.” So we might construe propositions as effects brought about by minds. More specifically, they would be effects that result from joining together various ideas or concepts and intending that some state of affairs obtains or doesn’t obtain. Paul M. Gould and Richard M. Davis elaborate:

“And just as there cannot be thoughts without a thinker, ideas (which are nothing but materials for thinking) cannot exist apart from the minds that have them. But then what better explanation could there be for the orderly arrangement of ideas than the mental activity of thinkers? The obvious conclusion to be drawn here is that the things properly said to be true or false (propositions) actually result from mental activity –from the joining or separating of ideas….Thus it follows straight away that propositions are mental effects. For propositions have parts, those parts are best construed as ideas, and their being properly related (that is “fitted into” truth claims) requires a mental arranger.” (See Beyond the Control of God, ed. Gould, p. 58)

Thus to form the proposition ‘Dwight Goodyear turned 47 years old in 2017’ a mind would, on the one hand, have to join the concept of Dwight Goodyear with the concepts of 47, year, 2017, and so on and, on the other hand, have to intend the result to be true. This view of propositions is known as conceptualism which Quentin Smith defines as follows: “Conceptualism with respect to propositions is the theory that it is necessarily the case that propositions are effects of mental causes. It is necessarily true that for any x, if x is a proposition, then x is an effect of some propositional attitude.” (Faith and Philosophy, Vol. 11, No. 1, p. 38).

Conceptualism is to be distinguished from other popular views that maintain propositions are sentences, abstract entities, or beliefs. Sentences, unlike the propositions expressed by them, are not intentional insofar as they are arrangements of non-intentional material like ink, lead, pixels, etc. As such, they cannot be true or false. To be sure, we might metaphorically ascribe a form of derived intentionality to them (as we do when we see a word that appears to be spelled in the sand by the non-intentional movements of waves and sea shells). But ultimately they are the physical means by which we express propositions that, because they are the effects of minds, have intrinsic intentionality. What about abstract entities like numbers? Can they be true or false? Well, one plausible view of abstract entities requires them to be inert, immaterial, non-mental things that do not enter into causal relations. But if this is the case they do not have the mental intentionality needed to be true or false. And beliefs, while more promising insofar as they are mental in nature, are probably best understood as attitudes towards propositions rather than being the bearers of truth and falsity themselves: if I believe I am 47 years old in 2017 then I have an affirmative attitude towards the proposition ‘Dwight Goodyear turned 47 years old in 2017.’

If this approach to propositions is plausible, then any presentation of an argument would require, along with the laws of logic, at least the following:

(1) Minds with intentionality.

(2) Concepts that can be joined together to form propositions.

(3) Propositions that result from this joining together of concepts which can be true or false.

(4) The ability to relate propositions to one another as we do when we infer ‘Socrates is mortal’ based on the propositions ‘all humans are mortal’ and ‘Socrates is a human.’

Now, substance dualism is the view that humans are comprised of two radically different types of substances that interact but can, in principle, exist independently from each other. One popular version of substance dualism maintains that the mind is a non-physical, simple (not made of parts), and non-spatial substance whereas the body is a physical, complex (made of parts), and spatial substance. I think an interesting defense of substance dualism can be developed based on the above analysis of propositions. Here is just a brief sketch of how this justification might work that takes into account points (1)-(4):

(a) Individual propositions or judgments (for example, ‘a triangle is not a square’) and the concepts that go into making up propositions or judgments (for example, the universal ideas of triangularity and squareness which, as universal, cannot be located in a particular place) cannot be accounted for if we are just complex bodies in space. But if we are also simple and non-spatial minds, perhaps we can think universal concepts and join them together. James Royce, in his book Man and His Nature (McGraw-Hill, 1961), elaborates:

“Matter excludes other matter from occupying the same space; these acts [of making judgments] show a compenetration, a disregard for the limitations imposed by quantity, which can only be due to the fact that they are not spatial. My concept of a triangle cannot be measured. I can have larger and smaller images, but the idea of what a triangle is applies equally well to all triangles, large and small, which could not be possible if the idea had size itself. My idea of an elephant is no bigger than my idea of a flea, for neither is quantified. Ideas do not occupy space: not having parts, they cannot extend over quantified matter. Nor does a simple idea occupy many parts of the brain at once, for then we would have many ideas, not one, of any one thing. A judgment means recognition of identity or non-identity of two concepts; but if one concept is in one space, and the other in another part, I could never get the two together in a judgment. The only conclusion is that the ultimate subject of such simple operations is itself simple.” (p. 313)

(b) And what about the relations between propositions that must exist if we are to construct arguments and make inferences? When we reason one mental state seems to cause another mental state by virtue of its propositional content or meaning. We grasp the meaning of the proposition ‘All humans are mortal’, grasp the meaning of ‘Socrates is a human’, and then, based on our mental apprehension of this propositional content, infer the conclusion ‘Socrates is mortal’. This appears to be a form of rational causation which depends on the mind and its apprehension of propositions and propositional content. But physical causation is only a matter of energy interacting in accordance with the basic forces and laws of nature. It has nothing to do with propositions and their content at all. Indeed it would seem, as Edward Feser nicely put it, “that the electrochemical properties of the neural processes with which the thoughts are associated are entirely sufficient to bring about whatever effects they do bring about. The meaning or content of the thoughts is irrelevant” (see his Philosophy of Mind p. 152). Tyler Burge elaborates:

“[R]eason is a constitutive structural feature of causation by propositional psychological states and events. According to the natural sciences, reason is not a structural feature of material composites. The causation by material parts of material composites, operating in their physical relations to one another, must suffice to alone compose causation by material composites. It is hard to see how the causal powers and causal structure of material components could alone compose the causal powers and causal structure of causal transactions that hinge on the rational, propositional structures of propositional states and events. So it appears that rational, propositional, psychological causation is not the causation of a material composite.”


“The second concern about compositional materialism is similar, but does not feature causation. Here it is: the physical structure of material composites consists in physical bonds among the parts. According to modern natural science, there is no place in the physical structure of material composites for rational, propositional bonds. The structure of propositional psychological states and events constitutively includes propositional, rational structure. So propositional states and events are not material composites.” (see his article “Modest Dualism” in The Waning of Materialism, eds. Koons and Bealer).

So far we can conclude that universal ideas, propositions, and rational causation are not a function of material composites. Since we think universal ideas, form propositions, and infer one proposition from another when we argue, then our minds must be simple, immaterial, and irreducible to the complex material structures of the brain. To these points we can add two more:

(c) We have seen that one plausible way to construe propositions is as intrinsically intentional. But intentionality is purposeful and thus incompatible with the purposeless movements of matter in motion and the non-teleological explanations (explanations that make no reference to purpose) widely embraced in contemporary physics, chemistry, and biology. Thus intentionality would be a function of our non-physical minds not our brains.

(d) We have also seen that propositions are the bearers of truth and falsity. But physical facts are not true or false: they are simply states of affairs in the world. We don’t say a desk in front of us is true or false; what we intentionally assert about the desk, namely a proposition, is true or false. So if we are thinking propositions that can be true or false at all, including the proposition ‘substance dualism is false’, then we wouldn’t be reducible to any set of physical facts including the set that makes up the totality of the brain.

So if we are presenting and analyzing arguments then brains, no matter how complex, wouldn’t be enough to account for this activity: we would also require non-physical, simple, and non-spatial minds. Substance dualism, unlike property dualism which accepts, on the one hand, that mental properties are not physical and, on the other hand, denies they are properties of a substance, can offer us an account of these minds for at least three reasons:

(1) According to property dualists, mental properties are an epiphenomenon of brain activity, that is, they are effects that have no capacity to cause effects themselves. To borrow a metaphor from Williams James, epiphenomenal properties would be like the shadows that accompany a traveller. But if we are substances then we may be beings capable of action. As G. W. Leibniz put it in the first line of his Principles of Nature and Grace, “A substance is a being capable of action.” And this capacity seems required if we intentionally form, assert, deny, connect, infer, analyze, and justify propositions that can be true or false. Moreover, the action that marks critical thinking is best understood as action that flows from a free will or one with the ability to choose from among real alternatives and justify the one that appears the most sensible. 

(2) It is hard to see how we can identify intentional propositional events without identifying a thinker to whom these events belong. After all, who would be doing the intending, inferring, and evaluating in the process of critical evaluation? Recall the quotation from Gould and Davis: “And just as there cannot be thoughts without a thinker, ideas (which are nothing but materials for thinking) cannot exist apart from the minds that have them.” And thinkers are best understood as active substances with intrinsic intentionality rather than collections of mental properties with no power to act at all.

(3) We have seen how reasoning requires a simple subject. As Royce put it: “A judgment means recognition of identity or non-identity of two concepts; but if one concept is one space, and the other in another part, I could never get the two together in a judgment. The only conclusion is that the ultimate subject of such simple operations is itself simple.” And substance dualism, unlike property dualism which leaves us with a multitude of disunified mental properties, provides this simple subject that allows us to make sense of the unity we find in propositions and their relationships.

Given all these points, we can formulate a valid hypothetical syllogism for substance dualism from the fact of argumentation:

Premise 1: If we are arguing then we require propositions and rational causation based on propositional content.

Premise 2: If propositions and rational causation based on propositional content exist then substance dualism is true.

Conclusion: So if we are arguing then substance dualism is true.

The benefits of accepting this conclusion are not confined to accounting for reasoning. For if we are immaterial, unified substances that can act based on rational deliberation then we can make some sense of morality as well. After all, to be held accountable for our actions in the just deserts sense seems to require that we can freely deliberate before choosing and that we are, in some fundamental sense, unified persons over time. Moreover, substance dualism casts a new light on the nature of death. If the soul is simple, if it is not made of physical parts, then it may be indissoluble. And if it can function apart from the body by thinking immaterial universals then perhaps it can exist apart from the body. These points suggests that an afterlife for a reasoning mind may be possible. In doing so, they show substance dualism may have religious implications however mysterious.

However, substance dualism certainly has its share of problems. For example, where do these immaterial substances come from? How does one immaterial mind pair up with one particular body? Do we really want to accept a theory so inconsistent with the prevailing naturalism of the sciences? Don’t various forms of brain damage show we are made up of material parts after all? And how can a non-physical mind interact with a physical body? These are tough questions. But it is important to understand there are plenty of plausible responses to them (for some, see the links below as well as a helpful overview of dualism here). Those convinced by some of these responses might embrace substance dualism as an account of human rationality which, rather than rationally explaining away our rational lives in a typically self-defeating fashion, attempts to explain them and connect them to our moral and religious sensibilities as well. 

For more on the claim that brains, no matter how complex, wouldn’t be enough to account for reason go here for Plato’s Wooden Horse Argument.

For Leibniz’s argument that no analysis of the brain, however complex, can account for the unity of perception, go here.

For Leibniz’s thoughts on propositions, the soul, and God, go here

For my post on the brain as receiver of the soul’s activities which may survive brain damage and even have an afterlife, go here

For some thoughts on the interaction problem between mind and body in relation to quantum mechanics, go here

For an account that truth is not a function of human minds alone, go here.

For an argument that critical thinking requires free will and thus a substantial mind to choose, go here.

For an argument for God’s existence from the existence of necessary truths, go here.

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