We have now seen what the Rationalists considered to be the most certain truths and why. But what is it that is supposed to give such ideas their certainty? It may seem ludicrous to question why it is that we believe that 2 + 2 = 4, or that "Black is not white", but if we are trying to find reasons for knowledge (as the Rationalists are), we may feel entitled to ask this question.

The answer Descartes gives relies on what he calls the clarity and distinctness of an idea. What does this mean? The explanations that Descartes himself gives are not all that clear and distinct. What he says can be summarised as follows:

a) An idea is clear if we cannot help taking notice of it. Examples of this would be strong physical sensations, such as pain, or thoughts, such as the desire for something.

b) An idea is distinct if it cannot possibly be confused with anything else. Some ideas, such as toothache, are clear (we must take notice of it), but indistinct (in that we can be unsure of exactly where the pain is).

Descartes also claimed that an idea could be clear without being distinct, but could not be distinct without first being clear. This is because if an idea were distinct enough not to be confusable with other ideas, this would also single it out so that we could not help being aware of it.

Discussion

Is there anything clear and distinct about the concept of clear and distinct ideas?