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….
In the Meditations, Descartes seeks to prove the existence of the external world in a series of five dialectically linked proofs. The first, in the so-called painter analogy of the First Meditation, investigates whether our ability to have dream representations (likened there to paintings of objects) presupposes acquaintance with material objects external to the mind, finding that it does not. What is presupposed, rather, is that there is a class of “simpler and more universal things … [which] include corporeal nature in general, and its extension; the shape of extended things.” These things “are as it were the true colour from which we form all the images of things” and play this role “whether they really exist in nature or not” (AT VII 20, CSM II 14).
The second and third attempts take place in the Third Meditation, comprising two different applications of causal principles to ideas, the first (paras. 8–11) to ideas considered “materially,” that is, as mental occurrences (“method 1”); the second (paras. 12–21) to ideas considered “representatively,” that is, as mental occurrences that represent one thing rather than another (“method 2”). The first method fails largely because of the possibility that there is inside me a capacity (“faculty”) for producing sensory ideas, as there apparently is in the case of dreams.
The second method contains the heart of Descartes’ causal epistemology, most perspicuously formulated in Axiom V of the Geometrical Exposition in the Second Replies: “The objective reality of our ideas needs a cause which contains this reality not merely objectively but formally or eminently.” The objective reality of an idea seems to be a reality that Descartes attributes to objects of our ideas regardless of whether those objects actually exist, and the formal containment of the reality is attributed to objects when they actually exist (see being, formal versus objective). There is a controversy about what “reality” refers to: Does it refer to a metaphysical category like being a finitesubstance or does it refer to a specific property, like being an intricate machine of a particular kind?
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