Substance is that which has no dependent relation on any other; and unlike an atom, is infinitely differentiable - it has parts; and those parts thus distinguished have relations amongst themselves; and are subject to change (Lucretious on atoms: that which has no parts is not subject to change and is permanent).

Descarte introduced res cogitans and res extensa which is generally translated as 'thinking substance' and 'extended substance'; but it's in the notion of 'substance' by which dependence is not an possibility - thus from here, directly we have mind/body dualism; in the sense of being entirely distinct and without effect on each other.

This goes against what we observe 'clearly and distinctly': mind acting on body - I pick up a stone, and body acting on mind, I duck a stone flung in my direction.

Is substance then the correct translation for res? And what how did Descarte himself suggest their dependence? If he did.

From item 52 from his Principles:

As for corporeal substance and mind (created thinking substance); they can be understood in terms of a single common concept, namely this one: things that don't depend on anything for their existence, except God.

This suggests that Descartes isn't conceiving substance in the classical form; the question is where he derives his notion of res in this sense; is he deriving it from earlier Scholasticism?

  • 1
    You probably know this infamous bit of trivia, but Descartes suspected mind-body interact through the pineal gland. And certainly he could not use the term res in a "classical" sense, given his fudge factor, the active God of the gaps. Commented Sep 11, 2015 at 13:30

3 Answers 3


The short answer is "yes". For Descartes the res is a substance on its own, and the term did derive from scholasticism.

In the scholastic jargon, "res" (which literally just means "thing") was first used to be the name of any kind of entity whatsoever, be it a substance, an accident, a transcendental principle (such as unity, goodness, etc.). The term evolved in the context of a debate about the subject matter of metaphysics. What is metaphysics about? Aristotle says both that the subject matter of metaphysics is substance and that the subject matter of metaphysics is reality in general, being qua being. Briefly, the idea of the term "res" is that you can say that everything that is a res is part of the study of metaphysics in some way. Either because the thing you are talking about is a substance, or the principle of a substance, or an accident of a substance, etc.

In Descartes's usage though, it is clear that the res extensa and the res cogitans are both substances, less because of the use of the word "res" and more just because of the way Descartes describes both. The crucial fact is that Descartes thinks they can exist independently of each other.


You can see Descartes' Modal Metaphysics : 5. Real Distinction :

A thing is complete, for Descartes, when it is a substance:

[B]y a ‘complete thing’ I simply mean a substance endowed with the forms or attributes which enable me to recognize that it is a substance. (AT 7:222, CSM 2:156)

Since a Cartesian substance is a thing that is ontologically independent (Principles, I:51–52), a complete thing is an ontologically independent thing. When we clearly and distinctly perceive mind and body to be complete, we know that they are substances. When we still clearly and distinctly perceive them to be substances after clearly and distinctly perceiving them apart from each other, we know that they are not the same substance under different descriptions.

On this view, Descartes holds that mind and body are ontologically independent substances, and their distinctness consists in their ability to continue to exist even after God separates them.

  • +1: for the reference; but also Spinoza is understood to have completed Descartes system; and there the res extensa and cogitans are modes of a substance; it makes me suppose there is some other seed in Descarte that propelled Spinoza along that angle. Commented Sep 10, 2015 at 20:04
  • Later, for example in the same entry: 'an alternative reading of their real distinction between mind and body reads the distinction as their ontological independence but not their separability'; Commented Sep 10, 2015 at 20:12
  • 2
    @MoziburUllah - see Spinoza's Modal Metaphysics and Spinoza's Theory of Attributes. Commented Sep 11, 2015 at 7:31

Res Cognitans and Res Extensa when considered as two things creates the concept of duality. The cosmic energy and the earthly ingredients when conjugate life is the phenomenal outcome. But if we consider even the earth a result of cosmic consciousness this conceot of duality disappears. It is Res Cognitans only.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .