Descartes’ Substance Theory and Mind-Body Dualism

Posted on Feb 5, 2025 in Philosophy and ethics

Descartes’ Theory of Substance and Mind-Body Dualism

In all areas, Descartes defined substance as that which exists in such a way that it does not need anything else to exist. He distinguished three types of substance:

  • Spiritual or Thinking Substance:
    • Infinite: God. Has no parts, so it is infinite.
    • Finite: Soul, a spiritual substance, but finite.
  • Extended or Material Substance.

Descartes’ ultimate aim was to safeguard the autonomy of the soul with respect to the subject. Classical science, imposing a mechanistic and deterministic conception of the material world, left no place for freedom. Freedom could only be safeguarded by subtracting the soul from the need for the mechanistic, which required placing it as a sphere of autonomous and independent reality of matter. This independence of mind and body is the central idea provided by the Cartesian notion of substance. The autonomy of the soul with respect to the subject is justified by the clarity and distinction with which the intellect perceives the independence of both.

Relations Between Soul and Body

Descartes holds that the soul and the body communicate through the pineal gland by animal spirits.

Doubt and the First Truth (4th Part of the Discourse on Method)

The Methodical Doubt

Understanding has to find within itself the basic truths from which it is possible to deduce the entire edifice of our knowledge. This starting point must be an absolutely certain truth, which it is not possible to doubt. Finding such a starting point requires a previous task: to eliminate all the knowledge, ideas, and beliefs that do not appear endowed with absolute certainty. Everything that can possibly be doubted must be removed. Thus, Descartes begins with doubt. This doubt is methodical; it is a requirement of the method at the analytic stage.

Reasons to Doubt

  1. Fallacies of the Senses: The senses sometimes deceive us, and could they always deceive us? Yes, so the senses must be set aside.
  2. The Impossibility of Distinguishing Wakefulness from Sleep: It may be that all we know is a dream.
  3. There are Times When We Err in Reasoning: Therefore, whenever we reason, we can make mistakes. Thus, reasoning itself is doubted.
  4. The Possibility of an Evil Genius: Perhaps there is some evil spirit of extreme power and intelligence, which makes every effort to induce error. This evil genius hypothesis assumes that perhaps the human mind is such that it is always and necessarily wrong when it attempts to grasp the truth. This is an unlikely scenario, but it allows us to doubt our knowledge.

The First Truth and the Criterion

Doubt seems doomed inevitably to skepticism. However, Descartes found absolute truth, immune to doubt, however radical: the very existence of the subject who thinks and doubts. If I think the world exists, maybe I am wrong about the existence of the world, but there is no error in that I think. I can doubt everything, but I cannot doubt that I doubt. My existence as a thinking subject is free from error or possible doubt: “I think, therefore I am” (Cogito, ergo sum).

The Thinking Self

My existence as a thinking subject is not only the first truth and the first certainty, but it is also the prototype of all truth and certainty because it is perceived with great clarity and distinction. Whatever is perceived with equal clarity and distinction will be true and can be stated with unwavering certainty. Therefore, it can be set as a general rule that whatever I perceive clearly and distinctly is true.

Ideas

Ideas are the object of thought:

  1. We already have an absolutely certain truth: the existence of the self as a thinking subject. The undoubted existence of the self seems *not* to imply the existence of any other reality. Although I think, maybe the world does not exist in reality; the only certainty is that I think that the world exists.
  2. Descartes has no choice but to infer the existence of reality from the existence of thought. “I think”; all of our knowledge has been removed, including knowledge of the existence of extra-mental reality.