In the Third Meditation, Descartes distinguishes two main subclasses of “thoughts”: “ideas,” which are “as it were images of things,” and others, “thus when I will or am afraid, or affirm or deny” (AT VII 37, CSM II 25–26). The latter, “judgments,” “can properly be said to be the bearers of truth and falsity.” Descartes will later call this kind of falsity “formal falsity” (AT VII 43, CSM II 30). He goes on to say that, “as far as ideas are concerned, provided they are considered solely in themselves and I do not refer them to anything else, they cannot strictly speaking be false.” Thus, it is only judgments “where I must be on my guard against making a mistake.” If we suppose that Descartes also means that ideas cannot properly speaking be true, then we have a bifurcation thesis: some thoughts can be the bearers of truth and falsity (properly understood); others cannot. Call this the “standard view.” The standard view also comes with an explanation for the bifurcation. Since only propositions can be true or false and since judgments are expressed by statements with propositional clauses (e.g., “I judge that God exists”) and ideas are expressed by phrases with term structures (e.g., “an idea of God”), judgments can be true or false, but ideas cannot be.
There are some difficulties with the standard view. For one thing, when in the Fourth Meditation, Descartes explains the difference between judgments and ideas, he does not mention a distinction between term expressions and proposition expressions but says that judgments are active events, falling on the side of the will, and ideas are passive events, falling on the side of perception (AT VII 56, CSM II 39). For another, there are several categories of texts in which Descartes attributes truth to items that fall on the side of perceptions rather than judgments. One of the most important of these is where Descartes asserts his “rule of truth,” for example, in the second paragraph of the Third Meditation: “Whatever I perceive very clearly and distinctly is true.” If perceptions are not judgments, how can they be true? The answer that the standard view offers is that they can be true if the content of the clear and distinct ideas is a proposition, which in this case it is: “I am a thinking thing….