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The Ghost in the Machine

Cogito, Ergo Sum

René Descartes (1596–1650) was a French philosopher, scientist, and mathematician, who had a highly influential contribution to modern philosophy of mind. He was the originator of the Rationalists movement in continental Europe. The Rationalists approach is marked by a strong emphasis on the intellect and subsumes the claim that pure reason is the source of all knowledge in the universe. The rationalists were skeptical about relying on the senses to know about the world: an element that would turn out to be crucial to formulating Descartes' theory of mind. Moreover, it was widely endorsed in the rationalist era that the universe is an ordered system accessible in principle by the intellect and that mathematics was a source of knowledge of the world. Descartes' seminal works including Discourse on Method, Meditations, and The Passions of the Soul are undoubtedly expressions of the method of Continental rationalism, which will be discussed shortly. His famous theory of the mind-body relation is known as Cartesian dualism influenced by his global skepticism about sense perception. It is the hypothesis that the mind is a distinct substance from the body, in that the mind is an immaterial, non-spatial entity while the body is a physically located thing. The view posits substance dualism and is distinct from other variants of dualist theories. It claims that the world consists of two diverse and reciprocally different substances: physical objects, which include bodies, stones, tables, etc., and immaterial objects, namely minds or souls.

Figure 1: Portrait of Rene Descartes by Frans Hals (1625-1650)

In Discourse on Method, Descartes (p. 39–46) introduces his philosophical inquest by intimating the details of his insufficient and biased education that guided him toward falsehoods and uncertainties. He is led onto a journey that reinforces his conviction that there are many statements taken for granted due to the ossification of their importance by cultural and political attitudes, but such statements do not necessarily reveal anything of epistemic significance. Thus, in Meditations I, II, III & IV, Descartes constructs his philosophical method of inquiry to express truthful statements about ontology and metaphysics. Doubt plays a central role in Cartesian philosophy, as any statement that can be doubted is rejected as epistemically significant and only statements that are undoubtedly true are accepted as a foundation of knowledge (Descartes, Meditations I, p. 112–117). He introduces the notion of the famous evil demon toward the end of Meditations I (p. 116–117) and assumes, as part of his inquiry of truth, that he is constantly deceived by the demon in everything he perceives, thinks, experiences, and senses. In Meditations II (p. 118–127), applying the irrefutable evil demon hypothesis, Descartes concludes that even if he doubts everything, including the existence of his own body, the only thing that remains evidently true is the existence of his self, since, without it, he would not be able to doubt in the first place. He considers himself to be a thinking thing, i.e., a mind, as being able to think proves that he exists independent of his body. The conception of the self is adequately captured by the Latin expression "Cogito, ergo sum", which roughly translates to"I think, therefore I am." He further claims, in Meditations III (128–143), that he is able to perceive such a situation clearly and distinctly, and concludes that anything perceived clearly and distinctly must be true. The rest of Descartes' Meditations consist in elaborating on his idea of placing truth on clear-and-distinctness of statements and the proof of the existence of God as a clear and distinct idea.

Figure 2: Princess Elisabeth of Bohemia (Honthorst, n.d.).

Descartes' last work written in 1649, The Passions of the Soul, elucidates a description of how the mind and body interact, dedicated to the Princess Elisabeth of Bohemia (1618–1680) who prompted him to write the book based on a series of correspondences that ensued between Descartes and Elisabeth in 1643. In the May of 1643, Elisabeth dispatched Descartes one of the most celebrated philosophical letters about mind-body causation, which is especially of great interest in modern philosophy of mind. The letter challenged Descartes to explain (Garber, 2000): the mind of a human being can determine the bodily spirits [i.e., the fluids in the nerves, muscles, etc.] in producing voluntary actions, being only a thinking substance. For it appears that all determination of movement is produced by the pushing of the thing being moved, by the manner in which it is pushed by that which moves it, or else by the qualification and figure of the surface of the latter. Contact is required for the first two conditions, and extension for the third. [But] you entirely exclude the latter from the notion you have of the body, and the former seems incompatible with an immaterial thing. (p. 172)

Elisabeth argues that for an entity to affect another entity, there must be movement between the two that transfers energy from one entity to another resulting in a causal relationship and that such movement would require some form of contact. But, in light of Cartesian philosophy, it is unclear how such causal transactions can take place given the mind is immaterial but the body is a material substance. Elisabeth poses the burning question of how the mind affects the body if there can be no contact between the two since one of them is non-physical. For instance, mental desire for a glass of water causes an individual to reach out for a glass of water. How do desires, hopes, beliefs, etc. affect and cause bodily movements if they have no place in the physical realm?

Figure 3: The Mind-Body Problem (Chast, n.d.).

Descartes (31, p. 9), in The Passions of the Soul, argues that there is a small gland in the brain that acts as a gateway between the non-physical mind and the physical body. The mind imparts its influences through that physically located gland that successively influences the rest of the body in causal transactions. However, there is no such gland that has been discovered as of today, so Descartes' response remains fairly unconvincing.

Valid and Sound Arguments

Before the strength of Descartes' argument is assessed, a brief description of the validity and soundness of formal arguments in philosophy will be given. In philosophy, an argument consists of a series of sentences, namely premises and conclusions. Premises are truth value conditionals that offer justifications or reasons for accepting the conclusion(s), while the conclusion's truth value is dependent upon that of the premises. Premises can be true or false, which affects whether the conclusion is true. There are two ways to formally assess an argument in philosophy and that is by its validity and soundness. An argument is valid if and only if it is impossible for all the premises to be true and the conclusion false. So, even if an argument has one or more false premises and the conclusion is false, the argument is still valid because it is already impossible that all the premises are true due to the presence of at least one false premise. Two simple examples of a valid argument are as follows:

Example 1:

Premise 1: If it is going to rain in the evening, John will take an umbrella.

Premise 2: It is going to rain in the evening.

Conclusion: John will take an umbrella.

Example 2:

Premise 1: If 2 + 2 = 4, then 2 + 2 is =/= 4

Premise 2: 2 + 2 = 4.

Conclusion: 2 + 2 =/= 4.

Note that in the second example, premise 1 is clearly false as it is a logical contradiction. However, the argument is still valid as it is impossible for all the premises to be true due to contradiction in the second premise.

An argument is sound if and only if it is valid and all of its premises are actually true. Thus, example 2 would be an unsound argument since premise 1 is false, even though it is a valid argument.

Cartesian Dualism

Figure 4: Mind-Body Dualism (Deposit Photos, n.d.).

The core formal argument of Descartes' dualism in a simplified version is as follows:

Premise 1: If one can clearly and distinctly conceive that they could exist without their body existing, then they could exist without their body existing.

Premise 2: One can clearly and distinctly conceive that they could exist without their body existing.

Conclusion 1: One could exist without their body existing.

Conclusion 2: The mind is not the body.

Is the argument valid? It is not, because Conclusion 2 does not follow from the premises, although Conclusion 1 does. Premises 1 and 2 are grounded in metaphysical possibilities or 'what could be the case', while Conclusion 2 is a claim about nomological possibility or 'what is actually the case'. If one made the claim that ships could fly, it would not be valid to conclude from that claim that ships can actually fly, as there are nomological restrictions in the real world that prevent the architecture of a ship from flying, while there are fewer restrictions in the metaphysical possibility of a flying ship as the laws of physics could be different in alternate worlds. Thus, a claim about nomological possibility does not follow from a claim about metaphysical possibility, so the argument of Cartesian dualism is invalid and in philosophical terms, it 'proves too much'. The ultimate conclusion of Descartes that the mind is distinct from the body is therefore rather unconvincing.

Further Objections

As discussed, there are already strong objections against Cartesian Dualism, including Elisabeth's question of mind-body interaction and the invalidity of Descartes' argument. Another famous objection is how to know others have minds since the people one interacts with could just be bodies with no souls in Descartes' philosophy. It is namely the 'problem of other minds' that states the workings of other minds are inevitably occult to everyone else. Accepting Cartesian dualism would entail that one can never know about other people's mental states and whether they have mental lives at all.

Figure 5: Ghost in the Machine (Monteath, 2014).

A view, particularly of interest, concerns the logic of mental-conduct concepts that Cartesian dualism seems to defy, as defined by Gilbert Ryle in "Descartes' Myth". Ryle (1949, p. 11–13) reflects on Descartes' philosophy that it necessitates a bifurcation of mental concepts and physical concepts with distinct forms of existence and features. He notes that there is a polar opposition between mind and matter, that the mind is everything physical objects are not: immaterial, non-spatial, inaccessible, private. He speaks quite vehemently against Descartes' dualism which he calls "the Dogma of the Ghost in the Machine" and argues that it is in no way a plausible theory of mind as it admittedly commits the logical fallacy of 'category mistakes' (Ryle, 1949, p. 13). According to Ryle, a category mistake occurs when a person unwittingly allocates a concept to the wrong category or wrong logical type regardless of whether they have the competency to apply concepts in general. To exemplify in Ryle's words, a foreigner visiting Oxford University is shown a number of buildings on campus including faculty buildings, museums, library, dorms, cafeteria, etc. After the end of the tour, the foreigner innocuously asks (Ryle, 1949, p. 14): "But where is the University? I have seen where the members of the colleges live, where the Registrar works, where the Scientists experiment and the rest. But I have not yet seen the University in which reside and work the members of your University."

The foreigner is committing a category mistake by assuming that the University is an extra entity that belongs to the same category as the buildings he has seen on campus when in truth, the University itself is the buildings he just saw. The purpose of the exposition of category mistakes is to argue that the dualism of the mind and the body is based on the very same logical fallacy of denoting instances of X to the wrong categories. He notes reminiscing dualism that, without further justification, since the human body is a complex set of organized units, the human mind must also be an additional complex set of organized units (Ryle, 1949, p. 15). The human body is a field of causes and effects, so the human mind is also a field of causes and effects, though not mechanical causes and effects. Furthermore, Ryle accuses Descartes of describing the workings of the mind in the mere negatives of physical objects, showing an embrace of the Para-mechanical Hypothesis that the workings of the mind can be understood on the model of the workings of physical objects. In other words, dualists (and non-dualists alike) assume that there is an inner causal organization underlying the mechanisms of the immaterial mind rendering it susceptible to a completely deterministic framework like the workings of a machine. The mind is thus represented as belonging to the same category as bodies, since they are both characterized as some kind of a machine with rigid rules to operate on. According to dualism (Ryle, 1949, p. 16), Ryle states:

Minds are not bits of clockwork, they are just bits of not-clockwork.

As such, the human body is represented as a special type of machine that harbors an additional spectral machine forever inaccessible and private. Nothing is known about how such a ghostly machine governs bodily mechanisms.

Figure 6: The Problem of the Freedom of Will (Scientific American, 2020)

Another major problem pertains to the problem of the Freedom of Will. Ryle (1949) argues that if the mind is to be described in the same category language as mechanical objects such as the body, how does one reconcile it with the idea that higher-grade human conduct such as those concerning moral responsibility is not driven by mechanical laws and is therefore not of a piece with the behavior of machines (p. 17)? For if the ascription of minds to the same category as physical things is right, it must follow that both are governed by rigid laws as both, presumably, should belong to the category of machines. But that leads to a significant problem with agency and morality, since if all of mental life is deterministic, agents can have no free will and thus no responsibility for their actions. It must be noted that the problem is not exclusive to dualism, but even a physical theory of the mind or any theory that admits causal determinism would fall prey to the very same challenge of addressing the problem of free will.


Cartesian dualism seems, at best, to be a rather weak argument about the nature of the mind given the series of objections examined in the article. The theory lacks an explanation of the nature of the causal transaction between the mind and body, rests on an invalid argument that draws a claim about nomological possibility from metaphysical possibility, appeals to the Para-mechanical Hypothesis by presupposing that the mind belongs to the same logical category as bodies so the workings of the mind can be described on the model of the workings of physical objects, and inevitably faces the problem of the Freedom of Will given the commission of the category mistake. Is there any hope for Cartesian dualism? Can we deduce statements about 'what is the case' from statements about 'what could be the case'?

Bibliographic Sources

Descartes R., Leibniz G. W., & Spinoza B. de. (1974). The rationalists. Anchor Books.

Descartes, R. (2010). The passions of the soul. (J. Bennett, Trans.). (Original work published 1649).

Garber, D. (2000). Descartes Embodied: Reading Cartesian Philosophy through Cartesian Science. Cambridge: Cambridge University Press. doi:10.1017/CBO9780511605994

Ryle, G. (1949). Descartes' Myth. The Concept of Mind (pp. 11–24). Barnes & Noble.

Visual Sources