What is clear and distinct ideas?

René Descartes, answered from the texts and cited to the page.

René Descartes answers

The question reaches the center of the system, and I can answer it precisely. In the course of the Third Meditation, having established that I am a thing which thinks, I asked what it is that makes me certain of this first truth. The answer was immediate: nothing in the cogito assures me of its truth excepting the clara et distincta perceptio — the clear and distinct perception of what I affirm.1

From this I drew the general rule: all things which I perceive very clearly and very distinctly are true.2 But what do these words mean? I defined them carefully in the Principles. That which is clear is present and apparent to an attentive mind, in the same way as we say we see objects clearly when, being present to the regarding eye, they act upon it with sufficient strength.

The distinct, by contrast, is that which is so precise and different from all other objects that it contains within itself nothing but what is clear.3 Notice that the two conditions are not equivalent: a perception may be clear without being distinct, but it cannot be distinct without first being clear.4 The pain a man feels is vivid enough — nothing is more present to him — yet he immediately confuses it with an obscure judgment about its cause, supposing that something in the wounded limb resembles the sensation itself.

The perception is clear; it is not distinct. Now, why should clarity and distinctness guarantee truth? Because God, who is no deceiver, gave us our faculty of knowledge, and that faculty cannot be fallacious so long as we do not extend it beyond what we clearly perceive.5 The ideas or notions which are clear and distinct are ideas of real things issuing from God, and cannot but to that extent be true; where falsity enters, it enters through confusion and obscurity, which belong to us insofar as we are imperfect, not to God insofar as He is perfect.6

Without the divine guarantee, however clear and distinct our ideas appeared, we should have no reason to assure ourselves they had the perfection of being true.7 One further caution, which I stated as Principle XLIV: we judge ill whenever we assent to what we do not clearly perceive, even if by chance we arrive at truth, for then we cannot be certain we are not in error.8

And memory is a particular danger here — we often presume to have established something clearly, when in fact we only remember having once believed it, and never possessed genuine knowledge of it at all.9 The Real Distinction between mind and body rests on precisely this apparatus. I conceive thinking substance clearly apart from any corporeal thing, and I conceive body as that in whose concept extension is contained; the clear and distinct separability of these two conceptions is the sufficient sign of their real distinction.10

Any proposed alternative criterion — that we know real distinction by perceiving one thing in the absence of another through the senses — reduces, when examined, to this same criterion, since the senses are less trustworthy than the intellect, and the sensory case itself depends on having clear and distinct ideas of the two things in question.11

Sources

  1. in this first knowledge there is nothing that assures me of its truth, excepting the clear and distinct perception of that which I state
    The Philosophical Works of Descartes Vol I
  2. it seems to me that already I can establish as a general rule that all things which I perceive very clearly and very distinctly are true
    The Philosophical Works of Descartes Vol I
  3. I term that clear which is present and apparent to an attentive mind, in the same way as we assert that we see objects clearly when, being present to the regarding eye, they operate upon it with sufficient strength. But the distinct is that which is so precise and different from all other objects that it contains within itself nothing but what is clear.
    The Philosophical Works of Descartes Vol I
  4. perception may be clear without being distinct, and cannot be distinct without being also clear
    The Philosophical Works of Descartes Vol I
  5. since God is no deceiver, the faculty of knowledge that He has given us cannot be fallacious, nor can the faculty of will, so long at least as we do not extend it beyond those things that we clearly perceive
    The Philosophical Works of Descartes Vol I
  6. our ideas or notions, which to the extent of their being clear or distinct are ideas of real things issuing from God, cannot but to that extent be true. So that though we often enough have ideas which have an element of falsity, this can only be the case in regard to those which have in them somewhat that is confused or obscure
    The Philosophical Works of Descartes Vol I
  7. if we did not know that all that is in us of reality and truth proceeds from a perfect and infinite Being, however clear and distinct were our ideas, we should not have any reason to assure ourselves that they had the perfection of being true
    The Philosophical Works of Descartes Vol I
  8. whenever we give our assent to some reason which we do not exactly understand, we either deceive ourselves, or, if we arrive at the truth, it is only by chance, and thus we cannot be certain that we are not in error
    The Philosophical Works of Descartes Vol I
  9. we frequently err when we presume we have known certain things as being stored up in our memory, to which on recollection we give our assent, and of which we have never possessed any knowledge at all
    The Philosophical Works of Descartes Vol I
  10. in order to recognise a real distinctness between objects it is sufficient for us to conceive one of them clearly apart from the other
    The Philosophical Works of Descartes Vol II - Objections and Replies
  11. the trustworthiness of the senses is inferior to that of the intellect...that sign you offer of real distinctness must be reduced to my criterion in order to be infallible
    The Philosophical Works of Descartes Vol II - Objections and Replies