One of the most profound and enduring legacies of Descartes' philosophy is his thesis that mind and body are really distinct, a thesis now referred to as "mind-body dualism" (Skirry, n.d.). He arrives at this conclusion by arguing that the nature of the mind is completely different from that of the body and, therefore, it is possible for one to exist without the other. In correspondence with Skirry (n.d.), this argument gives rise to the famous problem of mind-body causal interaction that is still debated today.
What is a Real Distinction?
It is important to note that for Descartes "real distinction" is a technical term denoting the distinction between two or more substances (Skirry, n.d.). A substance is something that does not require any other creature to exist while a mode is a quality or affection of that substance. Consequently, a mode needs a substance to exist and not only the concurrence of God. For example, having the form of a sphere is a mode of an extended substance. According to Skirry (n.d.), a sphere requires an object extended in three dimensions to exist: a non-extended sphere cannot be conceived without contradiction.
However, a substance can be understood to exist by itself without requiring any other creature to exist (Skirry, n.d.). For example, a stone can exist by itself. That is, its existence does not depend on the existence of minds or other bodies; and, a stone can exist without having any particular size or shape. According to Skirry (n.d.), this indicates for Descartes that God, if he wanted to, could create a world constituted by this stone by itself, further showing that it is a substance "really distinct" from everything else except God.
In short, in arguing for the real distinction between mind and body, Descartes is arguing that mind is a substance that can be clearly and distinctly understood without any other substance, including bodies, and that God could create a mental substance by himself without any other created substance (Skirry, n.d.). Thus, in correspondence with Skirry (n.d.), Descartes is ultimately arguing for the possibility of minds or souls existing without bodies.
Why Real Distinction?
What is the point of arguing that mind and body could exist without each other? What is the reward for going through each of the difficulties and enduring all the problems to which it gives rise? For Descartes, the reward is twofold (Skirry, n.d.). The first is religious in nature, since, it provides a rational basis for hope in the immortality of the soul. According to Skirry (n.d.), the second is more scientific in orientation, since, the total absence of mentality in the nature of physical things is fundamental to give way to Descartes' version of the new mechanistic physics.
Religious Motivation
In his Letter to the Sorbonne, published at the beginning of his seminal work, Meditations on First Philosophy, Descartes states that his aim in showing that the mind is really distinct from the body is to refute those "irreligious persons" who had faith only in mathematics and did not believe in the immortality of the soul without a mathematical demonstration of it (Skirry, n.d.). Descartes goes on to explain how, because of this, these people did not pursue moral virtue without the prospect of an afterlife with rewards for virtue and punishments for vice. However, since all the arguments in the Meditations are for Descartes absolutely true, as are the geometrical demonstrations, he believes that these people will be obliged to accept them. Therefore, according to Skirry (n.d.), irreligious people will be forced to believe in the prospect of an afterlife.
However, it should be remembered that Descartes' conclusion is only that the mind or soul can exist without the body (Skirry, n.d.). He does not go so far as to demonstrate that the soul is truly immortal. In fact, according to Skirry (n.d.), in the Synopsis of the Mediations, Descartes only claims to have shown that the decay of the body does not logically or metaphysically imply the destruction of the mind: further argumentation is required for the conclusion that the mind actually survives the destruction of the body.
This would involve both "an account of all physics" and an argument showing that God cannot annihilate the mind (Skirry, n.d.). However, in correspondence with Skirry (n.d.), although the argument from actual distinction does not go that far, it does, according to René Descartes, provide a sufficient foundation for religion, since, the hope for an afterlife now has a rational basis and is no longer a mere article of faith.
The Scientific Motivation
The other motive for arguing that the mind and body can exist without each other has a more scientific orientation, and derives from Descartes' intention to replace the final causal explanations of physics, which were considered favored by the late scholastic-Aristotelian philosophers, with mechanistic explanations based on the model of geometry (Skirry, n.d.). Although the merit of laying the foundations of this scholastic - Aristotelian philosophy, dominant at the time of Descartes, must be attributed to Thomas Aquinas, in correspondence with Skirry (n.d.), it is also important to note that other thinkers who worked within this Aristotelian framework, such as. Duns Scotus, William of Ockham and Francis Suarez, diverged from the Thomistic position on a sequence of important issues.
In fact, by the time of Descartes, scholastic positions diverging from Thomism were so widespread and so subtle in their differences that it was quite difficult to classify them (Skirry, n.d.). Despite this convoluted set of positions, according to Skirry (n.d.), Descartes understood that one thesis stood at the center of the whole tradition: the doctrine that everything ultimately behaved for the sake of some end or goal.
The Mind-Body Problem
The famous mind-body problem has its origin in Descartes' conclusion that mind and body are really distinct (Skirry, n.d.). The crux of the complexity lies in the assertion that the respective natures of mind and body are completely different and, in a sense, opposed to each other. According to this, in correspondence with Skirry (n.d.), the mind is a completely immaterial thing without any extension in it; and, conversely, the body is a completely material thing without any thought in it.
This means, moreover, that each substance can only have its own kind of modes (Skirry, n.d.). For example, the mind can only have modes of understanding, will and, in a sense, sensation, while the body can only have modes of size, shape, motion and quantity. However, according to Skirry (n.d.), bodies cannot have modes of understanding or will, since these are not modes of being extended; and minds cannot have modes of form or motion, since these are not modes of thinking.
According to Descartes, matter is essentially spatial, and has the characteristic properties of linear dimensionality (Westphal, 2019). Things in space have a position, at a minimum, a height, a depth, and a length, or one or more of them. Mental entities, on the other hand, do not have these characteristics. We cannot say that a mind is a two-by-two-by-two-inch cube or a two-inch-radius sphere, for example, located at a position in space inside the skull. According to Westphal (2019), this is not because it has some other shape in space, but because it is not characterized by space at all.
What characterizes the mind, according to Descartes, is that it is conscious, not that it has form or is made up of physical matter (Westphal, 2019). Unlike the brain, which has physical characteristics and occupies space. In short, in correspondence with Westphal (2019), our bodies certainly remain in space, and our minds do not, in the very direct sense that assigning linear dimensions and locations to them or their contents and activities is unintelligible.
The problem is that, in the case of voluntary bodily movements, contact between mind and body would be impossible given the non-extensible nature of mind (Skirry, n.d.). This is because the contact must be between two surfaces, but the surface is a body mode. Consequently, the mind does not have a surface that can come into contact with the body and cause the body to move. Thus, according to Skirry (n.d.), it seems that if mind and body are completely different, there is no intelligible explanation of voluntary bodily movement.
The consequences of this problem are very serious for Descartes, since it undermines his claim to have a clear and distinct understanding of the mind without the body (Skirry, n.d.). This is because human beings have sensations and voluntarily move some of their bodily members and this requires a surface and a contact. Since the mind must have a surface and a capacity for movement, the mind must also be extended and, therefore, mind and body are not completely different. This means that the "clear and distinct" ideas of mind and body as mutually exclusive natures must be false for mind-body causal interaction to occur. Thus, according to Skirry (n.d.), Descartes has not adequately established that mind and body are two really distinct substances.
Thus, Descartes' response to the mind-body problem is twofold (Skirry, n.d.). First, Descartes argues that an answer to this question presupposes an explanation of the union between mind and body. Descartes does not hold that voluntary bodily movements and sensation arise due to the causal interaction of mind and body by contact and motion. Rather, in correspondence with Skirry (n.d.), he maintains a version of the form-matter theory of the union between soul and body, endorsed by some of his scholastic - Aristotelian predecessors and contemporaries.
Secondly, Descartes claims that the question itself stems from the false presupposition that two substances with completely different natures cannot act on each other (Skirry, n.d.). Descartes argues that the less real cannot cause something that is more real, because the less real does not have enough reality to produce something more real than itself. According to Skirry (n.d.), this principle applies to the general level of substances and modes. According to this, an infinite substance, i.e., God, is the most real because it alone requires nothing else to exist; created and finite substances are the next most real, because they require only God's creative and conserving activity to exist; and, finally, modes are the least real, because they require a created substance and an infinite substance to exist.
Therefore, according to this principle, a mode cannot cause the existence of a substance, since, modes are less real than finite substances (Skirry, n.d.). In the same way, a created finite substance cannot cause the existence of an infinite substance. But a finite substance can cause the existence of another finite substance or a mode. Therefore, Descartes' point might be that the completely diverse natures of mind and body do not violate this causal principle, since both are finite substances that cause the existence of modes in some other finite substance. According to Skirry (n.d.), this further indicates that the "activity" of mind over body does not require contact and motion, thus suggesting that mind and body do not bear a mechanistic causal relation to each other.
References
Skirry, J. (s.f.) Descartes, Rene. Iep.utm.edu. Recuperado 11 November 2021, a partir de https://iep.utm.edu/descarte/
Skirry, J. (s.f.). Descartes, Rene: Mind-Body Distinction | Internet Encyclopedia of Philosophy. Internet Encyclopedia of Philosophy. Recuperado 9 de diciembre de 2021, de https://iep.utm.edu/descmind/
Westphal, J. (2019). Descartes and the Discovery of the Mind-Body Problem. The MIT Press Reader. Recuperado 9 de diciembre de 2021, de https://thereader.mitpress.mit.edu/discovery-mind-body-problem/
