THE TRUTH RULE AND THE PROBLEM OF THE CARTESIAN CIRCLE
Descartes writes in the second paragraph of the Third Meditation: “So I now seem to be able to lay it down as a general rule that whatever I perceive very clearly and distinctly is true ” (AT VII 35: CSM II 24). I call this principle the truth rule. In the third paragraph, Descartes decides that it is premature to take the truth rule to be established. He writes of “very simple and straightforward” propositions in arithmetic and geometry: “the . . . reason for my . . . judgment that they were open to doubt was that it occurred to me that perhaps some God could have given me a nature such that I was deceived even in matters which seemed most evident” (AT VII 36: CSM II 25). The matters that seem most evident, in the context of paragraph two, are beliefs based on clear and distinct perception, so that these beliefs (together with any that seem less evident) are themselves open to doubt. Descartes writes: “in order to remove . . . this . . . reason for doubt, . . . I must examine whether there is a God, and, if there is, whether he can be a deceiver” (AT VII 36: CSM II25). In the Third Meditation, Descartes offers an argument for the existence of a nondeceiving God. The truth rule is finally proved in the Fourth Meditation. Descartes concludes, on the ground that God is no deceiver, that “if . . . I restrain my will so that it extends to what the intellect clearly and distinctly reveals, and no further, then it is quite impossible for me to go wrong” (AT VII 62: CSM II 43).