Theories of Mind (Part 3): Descartes on Dubitability and Divisibility

Rene Descartes provided a number of arguments for the immateriality of the mind. For that requisite context, check out Part 1 and Part 2 in this series. Without further ado, let’s evaluate Descartes’ arguments from dubitability and divisibility.


2.2.2 Dubitability: Evaluation

Criticism One: A dilemma

A linguistic context is intensional precisely when it is not extensional. An extensional context is (for our purposes) present when the following condition is met:

(1) Necessarily, inter-substituted co-referring expressions preserve truth.

Condition (1) applies to scenarios in which an object has two names, N1 and N2. In such scenarios, one can formulate a true proposition about the object using N1. When condition (1) is met, if you substitute N2 for N1 into the proposition, the proposition cannot become false. In other words, such a substitution is truth-preserving. Because the object to which each name refers is identical, the words used to denote it simply don’t matter to proposition’s truth (in extensional contexts).

But (1) is not always met, and when it isn’t, the linguistic context is intensional. In intensional contexts, co-referring expressions cannot be substituted for one another without potentially changing the proposition’s truth value. The failure of (1) in intensional contexts derives from the fact that a single object can be presented to a thinking subject under different clusters of descriptions. Under such conditions, the agent in question may be unaware that the extramental referent of such clusters of descriptions is the same in each case.

In summary, an intentional object (else: linguistic expression) construed extensionally is the intentional object’s extramental referent, whereas an intentional object construed intensionally is the mind-dependent cluster of descriptions that the thinking subject associates with an object.

With the conceptual groundwork out of the way, a fatal dilemma now plagues Descartes’ argument. The intentional objects of Descartes’ doubt (the mind and anything material, respectively) are either construed intensionally or extensionally. If they are construed extensionally, then Descartes’ P1 is patently question-begging. For suppose that the mind is identical to something material. If that were true, then when Descartes claims he can doubt the existence of anything material, then since the extension of “the mind” (per hypothesis) is something material, it necessarily follows that Descartes can doubt the existence of his mind. Hence, when construed extensionally, the very claim that Descartes can doubt the existence of anything material but cannot doubt his mind’s existence presupposes from the get-go that his mind is immaterial, which is the very thing he aims to demonstrate. Therefore, when construed extensionally, Descartes’ P1 is question-begging.

But if the intentional objects of Descartes’ doubt are construed intensionally, then the argument is invalid since Leibniz’s Law breaks down in intensional contexts due to the fact that clusters of descriptions within subjects’ minds are not real, intrinsic properties of the extramental objects themselves. This is why we cannot infer the non-identity of the morning star and the evening star merely from the fact that, intensionally, one can know the morning star exists without knowing the evening star exists.

Therefore, Descartes’ argument is either question-begging or invalid. Either way, the argument is unsuccessful.

Criticism Two: The dubitability of the mind’s existence

Descartes holds that he cannot doubt the existence of his mind. But this is implausible. Descartes’ motivation for this is that doubting is a kind of thinking, and since thought presupposes a thinker to which the thought belongs, Descartes must be a thinking (and existing) subject. But it is not immediately evident that, necessarily, every thought must belong to a unified, thinking subject. It is at least conceivable that there exist a “Platonic Realm” wherein thoughts just “float,” as it were, not possessed by any unified, thinking, conscious subject. Moreover, there seems to be nothing inherently contradictory about this state of affairs. But if this is conceivable and at least not contradictory, then surely it is not certainly and indubitably true that, necessarily, every thought must belong to a unified, thinking subject. But if that is true, then Descartes’ claim that his mind is indubitably existent is false.


2.2.3 Divisibility: Evaluation

Criticism One: Question-begging

Suppose that the mind is, in fact, identical to the brain. If that’s the case, then it is simply false that the mind is indivisible — precisely because the brain is divisible. But this means that the very affirmation that the mind is indivisible amounts to the claim that the mind is not identical to the brain — and that is precisely the very issue in question. Hence, Descartes presupposes that the mind is not identical to the material brain (and/or body) in his very affirmation that the mind is indivisible. Hence, this very affirmation amounts to question-begging against the physicalist.

Descartes may respond that, although technically such a claim amounts to a denial of physicalism, the claim is validated by simple phenomenological inspection. For, according to Descartes, he apprehends the mind to be metaphysically simple.

But all Descartes has shown is that he is not aware of any parts composing his mind. But this is crucially different from and does not entail that he is aware that no parts compose his mind. Merely from the fact that, say, I am not aware of any neutrinos passing through me right now, that is crucially different from and does not entail that I am aware that no neutrinos are passing through me right now. But all Descartes has shown is the former, whereas his rejoinder to the question-begging allegation needs to establish the latter.

Criticism Two: Is the mind indivisible?

It is at least unclear whether the mind is indivisible. We know that severing the corpus callosum (the thick bundle of fibers that connects the two brain hemispheres) of epilepsy patients can, under certain experimental conditions, result in seemingly disunified, disparate perceptual experiences, desires, and even beliefs. It is unclear, therefore, that the mind is, after all, utterly indivisible.

The unity of consciousness as a difficulty for materialism

Despite the above criticisms, Descartes is nevertheless pinpointing a very serious difficulty for materialist accounts of the mind. Consider your present experience. You see a paper in front of you, feel its texture on your hands, and hear the rustling noise it makes. Neuroscience, though, has revealed that discrete neurophysiological events in the brain process each aspect of your experience (the shapes, sizes, colors, textures, sounds, motions, depths, and so on). “Yet,” writes philosopher Edward Feser:

The experience you are having is neither an incoherent jumble of distinct and disconnected features (pages, ink, motion, colors, etc.) nor is it a collection of distinct and disconnected experiences of distinct and disconnected features; it is a single, unified experience… The experience has a coherent significance or meaning, and significance or meaning for a single subject of experience. You are not only aware of the shape, texture, colors, etc. as separate elements, but are aware of them as a book; and it is you who are aware of them, rather than myriad neural events somehow each being “aware” of one particular aspect of the book.2

Despite the fact that the various aspects of our thoughts, perceptions, and so on are separately encoded by distinct neurophysiological processes, we nevertheless possess an integrated, unified, holistic experience rather than an awareness of a meaningless sequence of shapes, colors, motions, sounds, and textures. But how is this possible if the discrete neurophysiological processes exhaust all the facts of experience and thought? From whence comes this binding, this meaningful, continuous, unified conscious experience?

It clearly won’t do to hold that each disparate brain process is itself conscious, for that would not amount to a unified, integrated subject of conscious experience. Just as my experience right now of the color red and my roommate’s experience right now of a sweet taste is not sufficient for there to be a single, unified conscious experience of a red, sweet apple, the individual consciousnesses of the brain events would not by themselves add up to a single, unified conscious experience of a united scene. And surely things get even more complicated if the discrete parts themselves are utterly lacking in consciousness.

Nor will positing higher order neural mechanisms that integrate the information from lower order neural mechanisms solve the problem. “For now”, as Feser points out, “all the relevant information would have to be gathered together in this mechanism, which itself would be composed of yet further distinct neural processes encoding distinct aspects of the visual field, and the binding problem would arise again at a higher level.”3

This is not presented as an insuperable, knock-down problem, but it nevertheless carries weight as an explanatory impotence of materialist accounts of consciousness.

download-2In the next post in the series, we will examine a principle objection to Cartesian Dualism: the interaction problem.

Author: Joe


Note: References will be included in the last post in the series.


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