So many ideas...

Reading response for the Third Meditation: Explain why Descartes thinks that an idea itself cannot be false.  (This may involve saying something about what an idea is for Descartes.)  If ideas themselves cannot be mistaken, where and how does the possibility of error enter the picture?

Up to this point, Descartes has only established that he exists as a thinking thing. Now, as a thinking thing, he must think. But how can he know that the ideas that exist in his thoughts are true?  Descartes’ benchmark on the matter is that anything that he perceives vividly and clearly is true. He distinguishes two categories of ideas that he can perceive in this way: simple ideas, like mental images, and volitional ideas, like emotions, which can act upon other ideas. Both categories exist vividly and clearly in Descartes’ mind, so the ideas are true in his sense. But Descartes makes an important distinction. While the ideas themselves cannot be false as they exist in his own mind, he could make an error in judgment by attributing the cause of these ideas to something outside of his mind. While ideas could come from outside the self, it is also possible that they are innate or even invented. In this way, an idea could be true in the sense that it is present, vividly and clearly, in the mind, while one could be mistaken as to the source of that idea.