Descartes begins with one of the guiding dogmas of modernity: that the nature of the mind can be understood independently of anything else. As is often the case, the doctrine contains a certain amount of ontology masquerading as epistemology. If I can understand the nature of mind without understanding anything else, then the mind would be what it is if other things were different than they are—even if they differ to the point of becoming nonexistent. The dogma thus implies that mind can exist independently of anything else. It may in fact require other things in order to exist, such as a body—but that has no effect on its basic nature. Essence (here, of the mind) and existence are as separate for Descartes as they were for Aquinas.
Thus, at the beginning of the Meditations we find the cogito: I think, asserted without any specification of what I think. What are the objects of thought? If they are things in the world, and if to understand a thought includes knowing what it is a thought of, then my thoughts, and so my mind, cannot be understood without regard to objects in the world. The objects of thought must therefore themselves be thoughts: ideas.
Descartes’ own way of articulating this ontological implication of his guiding dogma is to say that a substance (such as the mind) does not depend for its existence on any other substance except God. This is stated later in the Meditations (III. ¶26), but is, I suggest, implicit from their outset.
If the mind is independent of all things except God, then a couple of further things follow. First, thought cannot be dependent on language—unless language is God. Some German Idealists (e.g. Hegel: see my The Company of Words) will take this kind of tack, but not Descartes. One problem with it, for monotheists such as Descartes will claim to be, is that languages come in the plural: we don’t think in language, but in a language, and for some reason there are always other languages around.
So language is not God, and thought cannot be bound to it. We don’t think in words, but in ideas, which are not words but (conveniently enough) word-meanings. This enables Descartes to drive a wedge between two meanings of the ancient Geek λόγος, thought and word. And it opens the way to the view that mathematics is a kind of thinking—indeed, is thought itself. For mathematics eschews words—but it is full of ideas.
Communication is now utterly distinct from thought, and we circle back to the guiding dogma: our minds are not dependent on other peoples’ minds or what we learn from them.
Moreover, if thought is mathematical, thinking is something only a select few can really do. Thus, in his “Reply to the Seventh Objections,” Descartes writes that “Only wise persons can distinguish between what is conceived clearly and what only seems and appears to be such” (Édtion F. Alquié, Garnier Vol. II 1967 p. 960).
This fits right in with philosophy’s ancient drive to exclusivity, its desire to make the “space of reasons” our space (#1). It is still traded on by philosophers today, in the wake of people like Hans Reichenbach: unless you think like we do, you are not fully rational.
The guiding dogma surfaces yet again with Descartes’ claim of continuous creation, the view that the activity by which God sustains the world from moment to moment is the same as the activity with which He created it. This follows from God’s immutability, Descartes’ open allegiance to which is elusive but presumably follows from his claim that “in the case of God, any variation is unintelligible” (Principles I.56) and a couple of other texts. If God acted one way in creating the world, and acts another way when He sustains it, He would hardly be immutable.
However Descartes gets to it, continuous creation means that because a being is dependent only on God, it is not dependent on previous states of the universe—including previous states of itself. The “just now” that Augustine feared (“make me chaste, but not just now”) has come to be ontologically basic; and the Latin for “just now” (modo) gave its name to this whole approach.
On the “modern” approach, and in particular in light of its view of continuous creation, nothing is path-dependent, and to understand anything is to explain it in terms of God alone. If God is immutable, then to understand anything is to reduce it to something immutable—a doctrine at least as old as Plato. The doctrine of continuous creation thus works out to a denial of empirical causality. The question then is whether later philosophers who deny causality—such as Hume, who located it entirely in the mind—fully escape the theological roots the denial has in Descartes. Is path-independence a theological notion?
Finally, the guiding dogma threatens to place Descartes in a position which is not only implausible, but unendurable, a mind which has access only to itself. Such a mind is prey to the paranoid fantasy of an Evil Demon, which infects it with false ideas; and even if we escape that fantasy, it seems that the mind may be completely alone, bereft of its body and of all human relationships. Hence the desperation with which, in the later Meditations, Descartes seeks to restore the world to knowledge, by appealing to divine veracity: if I am all there is, then God, in presenting me with the ideas of external things and people, is deceiving me—which He would never do.
We thus get the modern project that Hegel characterized as “throwing a bridge” between the mind and reality—a project which came to be called “epistemology.” Epistemology came inevitably (given the desperation on which it is founded) to be the first and basic philosophical discipline.
Modern philosophers, engaged in this project, differentiated themselves according to the side of the chasm from which they threw their bridge. The “rationalists,” like Descartes, worked from the side of mind, in virtue of their guiding dogma; the “empiricists,” such as Locke and Hume, worked from the side of nature, from the givenness to the mind of what is not the mind (i.e. “experience”). The contrast between the two came to be viewed in terms of the kind of thinking each side valorized rather than of the kind of objects they claimed could be known. The fact that both sides were trying, in their different ways, to vindicate a special kind of object, ousia, was covered over, and the social importance of philosophy was lost.