One of the most profound, significant, and long-lasting legacies of René Descartes' philosophy is the thesis that the mind and body are truly distinct entities, a claim now known as "mind-body dualism" (Skirry, n.d.). Descartes reached this conclusion after convincingly arguing that the nature of the mind is completely different from the nature of the body, implying that both could indeed exist independently of each other. According to Skirry (n.d.), this reasoning directly leads to the renowned problem of causal interaction between the mind and body, a topic that continues to be debated in contemporary philosophy.
What is a Real Distinction?
It is important to highlight that, for Descartes, the term "real distinction" is a technical concept denoting the distinction between two or more substances (Skirry, n.d.). In this context, a substance is defined as something that does not require any other entity to exist, while a mode refers to a quality or affection of that substance. Therefore, a mode needs a substance to exist, and not merely divine intervention. For example, the spherical shape is a mode belonging to an extended substance. According to Skirry (n.d.), a sphere requires an object that is extended in three dimensions to exist, as an unextended sphere cannot be conceived without logical contradiction.
On the other hand, a substance can exist on its own without depending on any other entity (Skirry, n.d.). For instance, a stone can exist independently, meaning its existence does not depend on the presence of minds or other bodies, and this stone can exist without having a specific size or shape. According to Skirry (n.d.), this implies that God, if He wished, could create a world composed solely of this stone, further demonstrating that it is a "really distinct" substance from anything else, except for God.
In summary, by arguing for the real distinction between the mind and the body, Descartes maintains that the mind is a substance that can be clearly and distinctly understood without recourse to any other substance, including bodies, and that God could create a mental substance independently of any other created substance (Skirry, n.d.). Thus, according to Skirry (n.d.), Descartes is ultimately defending the possibility that minds or souls could exist without the need for a physical body.
Why Real Distinction?
What significance might the argument that the mind and body could exist independently of each other have? What would be the reward for facing and overcoming each of the difficulties and enduring all the problems involved? For Descartes, the reward is twofold (Skirry, n.d.). The first reward has a religious nature, as it provides a rational basis for hope in the immortality of the soul. The second reward, according to Skirry (n.d.), has a more scientific orientation, as the complete absence of mentality in the nature of physical things proves fundamental for advancing Descartes' version of the new mechanistic physics.
Religious Motivation
In the "Letter to the Sorbonne," published at the beginning of his foundational work "Meditations on First Philosophy," Descartes expresses that his goal in demonstrating that the mind is distinct from the body is to refute those "irreligious people" who placed their faith solely in mathematics and did not believe in the immortality of the soul unless there was a mathematical demonstration to support it (Skirry, n.d.). Descartes goes on to explain that due to this lack of faith, such individuals did not seek to attain moral virtue, as they did not consider the perspective of an afterlife that would reward virtue and punish vice. However, since all arguments presented in the "Meditations" are as absolutely certain as geometric demonstrations, he believes these individuals will be compelled to accept them. Therefore, according to Skirry (n.d.), irreligious people will be forced to believe in the existence of an afterlife.
It is important to remember that Descartes' conclusion is only that the mind or soul could exist without the body (Skirry, n.d.). He does not prove that the soul is truly immortal. In fact, in the "Synopsis of the Meditations," he claims to have demonstrated that the decay of the body does not imply, either logically or metaphysically, the destruction of the mind; an additional argument would be necessary to conclude that the mind truly survives the destruction of the body. This would require both "a complete account of physics" and an argument demonstrating that God cannot annihilate the mind. Nevertheless, according to Skirry (n.d.), although the argument of the real distinction does not go that far, it provides, according to René Descartes, a sufficient basis for religion, given that the hope for an afterlife is now based on logical reasoning rather than merely an article of faith.
The Scientific Motivation
The other reason for arguing that the mind and body could exist independently has a more scientific orientation and stems from Descartes' intention to replace final causal explanations in physics, which were favored by Scholastic-Aristotelian philosophers, with mechanistic explanations based on the model of geometry (Skirry, n.d.). Skirry (n.d.) mentions that while Thomas Aquinas is credited with laying the foundations of this Scholastic-Aristotelian philosophy dominant in Descartes' time, it is also relevant to consider that other thinkers, such as Duns Scotus, William of Ockham, and Francisco Suárez, who worked within this Aristotelian framework, diverged from Thomistic positions on various important issues.
Indeed, during Descartes' time, Scholastic positions that diverged from Thomism were so widespread and subtle in their differences that classifying them was quite complicated (Skirry, n.d.). Despite this tangled array of positions, according to Skirry (n.d.), Descartes understood that a thesis lay at the core of the entire tradition: the doctrine that everything ultimately behaves according to some end or purpose.
The Mind-Body Problem
The famous mind-body problem originates from Descartes' conclusion that the mind and body are truly distinct (Skirry, n.d.). The complexity lies in the assertion that the respective natures of the mind and body are completely different and, in a way, opposed to each other. The mind is a completely immaterial entity, without extension, while the body is completely material, without the capacity for thought. This implies that each substance can only have its particular modes. 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, movement, and quantity. However, according to Skirry (n.d.), bodies cannot have modes of understanding or will, as these are not modes of extension; and minds cannot have modes of shape or movement, as these are not modes of thought.
Descartes claims that matter is spatial and has the characteristic properties of linear dimensionality (Westphal, 2019). Things in space have, at a minimum, height, depth, and length, or one or more of these dimensions. Mental entities, in contrast, do not exhibit these characteristics. It is not possible to describe the mind as a two-by-two-by-two-inch cube or a two-inch radius sphere, located in a position in space within the skull. This is not because the mind has some form in space, but because it is not characterized by space at all. What characterizes the mind is its consciousness, unlike the brain, which has physical characteristics and occupies space. In simple terms, according to Westphal (2019), bodies remain in space, while minds do not, in the most direct sense that assigning linear dimensions and locations to them or their contents and activities is unintelligible.
The problem arises because, in the case of voluntary bodily movements, contact between the mind and the body would be impossible due to the non-extended nature of the mind (Skirry, n.d.). This is because contact must be between two surfaces, but a surface is a mode of body. Consequently, the mind does not have a surface that can come into contact with the body and cause it to move. Therefore, according to Skirry (n.d.), if the mind and body are completely different, there is no intelligible explanation for voluntary bodily movement.
For Descartes, the consequences of this problem are serious, as they undermine his claim to have a clear and distinct understanding of the mind without the body (Skirry, n.d.). This is because humans experience sensations and move some of their bodily members voluntarily, which requires a surface and contact. Since the mind must have a surface and capacity for movement, it must be extended, and thus, the 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 incorrect to allow for mind-body causal interaction. Therefore, according to Skirry (n.d.), Descartes has not adequately demonstrated that the mind and body are truly distinct substances.
Thus, his response to the mind-body problem is twofold (Skirry, n.d.). First, he maintains that it is necessary to explain the union between mind and body, but does not believe that bodily movements and sensations are caused by direct interaction between mind and body. Instead, he defends a version of the form-matter theory about the relationship between soul and body, based on Aristotelian ideas. Second, he argues that the question itself is based on the false assumption that two substances with different natures cannot influence each other. He asserts that the less real cannot cause something more real, as it lacks the reality sufficient to produce something more real than itself. According to Skirry (n.d.), this applies to substances and their modes in general: an infinite substance, like God, is the most real because it needs nothing else to exist; finite substances require the activity of God to exist; and modes are the least real because they depend on a substance and the infinite substance to exist.
Thus, according to this principle, a mode cannot cause the existence of a substance, as modes are less real than finite substances (Skirry, n.d.). Similarly, a created finite substance cannot cause the existence of an infinite substance. However, a finite substance can cause the existence of another finite substance or a mode. Therefore, Descartes' argument could be that the completely diverse natures of the mind and body do not violate this causal principle, as both are finite substances causing the existence of modes in some other finite substance. According to Skirry (n.d.), this also suggests that the "activity" of the mind on the body does not require contact and movement, indicating that the mind and body do not maintain a mechanistic causal relationship.
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/
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