The Epistemological Turn
For the first two thousand years of Western Philosophy, the discussion of the nature of Being as such, which we have come to call "Metaphysics," was considered the foundation of all philosophy. Aristotle called the essays that we now label his Metaphysics "First Philosophy," meaning by this, as he himself said, those questions that are first in the order of being, not necessarily first in the order of knowing. Questions about the nature, conditions, and limits of human knowledge -- what we have learned to call Epistemology -- were treated by him as distinctly secondary, and of much less interest or importance. Aristotle consigned them to De Anima, very much the boondocks, philosophically speaking. There were always exceptions to these generalizations -- one thinks of the sceptic Sextus Empiricus, in whose writings some of Hume's arguments are anticipated. But to the profession as a whole, there was for two millennia no question that Metaphysics takes precedence over Epistemology, questions of Being having pride of place over questions of Knowing.
All that changed, abruptly and dramatically, with Descartes. Although his most important work is actually entitled Meditations on First Philosophy, thus echoing the traditional view, the very first paragraph of the First Meditation announces that Knowing will henceforth take primacy over Being:
"There is no novelty to me in the reflection that, from my earliest years, I have accepted many false opinions as true, and that what I have concluded from such badly assured premises could not be but highly doubtful and uncertain. From the time that I first recognized this fact, I have realized that if I wished to have any firm and constant knowledge in the sciences, I would have to undertake, once and for all, to set aside all the opinions which I had previously accepted among my beliefs and start again from the beginning."
There follow in rapid succession the famous doubts cast upon all things previously supposed to be true, culminating in the Second Meditation with the dramatic proclamation: "I must finally conclude and maintain that this proposition, I am, I exist, is necessarily true every time that I pronounce or conceive it in my mind."
Tanker trucks of ink have been spilled over this famous argument, and I do not intend to add to the torrent here. But I do want you to take note of certain central features of Descartes' startling break with his predecessors. I have already noted the reversal in the order of priority of Being and Knowing. In the next three centuries, Epistemology would become the Queen of the Philosophical disciplines, and Metaphysics, save in certain Thomist backwaters, would cringe in corners, grateful for a few crumbs of attention. Even more striking is the subjectivist turn, the turn inward to an examination of the instrument of knowledge, the mind, rather than the object of knowledge, the world. More and more, philosophers turned away from proofs of the existence of God or classifications of the categories of Being to an examination, an inventory, of the cognitive powers of the mind. The titles of the major treatises reveal this shift in focus: Rules for the Direction of the Mind, An Essay Concerning Human Understanding, A Treatise of Human Nature, and of course Critique of Pure Reason.
The general idea is that all assertions about the nature of Being [i.e., about substances, space, time, causation, the existence of God, and so forth] must be held hostage to an examination of the nature of Knowing, more precisely to an examination of the limits of the human mind's capacity to know the truths of those assertions, and indeed even its capacity to form the concepts in terms of which the assertions are framed. If the human mind is incapable of forming the concept of the infinite, or if it is incapable of apprehending an object adequate to the concept of the infinite, then it cannot possibly have knowledge of a being defined as infinite. Hence all Rational Theology must be set aside as consisting of claims that cannot justified. Notice that if one can form the concept of the infinite, then it may be possible to believe in the existence of an infinite being even if one cannot have knowledge of the existence or nature of such a being. This is what Kant means by his oft-quoted statement that he has limited knowledge to make place for faith.
The first and most important task of philosophy thus becomes an inventory of the powers, capacities, and limits of the mind, and this is in fact the form in which the Critical Philosophy is cast. Drawing on a long tradition of discussion of what were called "the faculties of the mind," Kant organizes his philosophy on the grand plan of a systematic inventory of the faculties of the mind: Reason, Understanding, Judgment, Sensibility, Imagination. In the full Kantian corpus, we find an examination of the theoretical employment of reason, an examination of the practical employment of reason, and an examination of the power of aesthetic judgment. Since each of these examinations is designed to ascertain whether the faculty in question can yield cognitively significant results, it is called a critique. So we have the First Critique, an examination of the theoretical employment of the cognitive powers of the mind; the Second Critique, an examination of the practical employment of the cognitive powers of the mind [i.e., their employment for action]; and the Third Critique, an examination of the power of Judgment in the making of aesthetic judgments [and also teleological judgments, but never mind that now.]
Even within each of these critical works, the organization is grounded in distinctions among the different cognitive powers of the mind. The Critique of Pure Reason offers us first a section devoted to the mind's receptivity for sensory content [The Transcendental Aesthetic],then a section devoted to the mind's capacity to form and employ concepts in the making of judgments [the Transcendental Analytic, with its two parts, the Analytic of Concepts and the Analytic of Principles], and then a section devoted to the mind's irresistible tendency to extend its legitimate capacity for organizing propositions into chains of deductive argument into ill-fated efforts to acquire universal and necessary knowledge of the independently real [The Transcendental Dialectic.]
Thus far, I am sorry to have to tell you, we are talking about the most superficial and least important level of Kant's thinking. All of this is merely classificatory and organizational, complicated as it may be. Things get vastly more difficult from here on, as well as very much deeper, philosophically.
Before turning to Kant's attempt to respond to Hume's sceptical criticisms of Newtonian physics, which, you will recall, is where we were when I paused to talk for a bit about the Epistemological Turn, I need to say just a few more words about Descartes, in preparation for Kant's deeper investigations. For Descartes, the defining characteristic of the mind is its capacity to form and assert judgments in consciousness. Even if these judgments are false, or if their truth cannot be known, nevertheless the mind is capable of forming them and asserting them. Hence, we may say that the most fundamental judgment a mind can formulate is simply "I think." Reflection on this elementary fact tells us that at its foundation, philosophy is a private, first-personal activity, carried on not by Reason as such but by an individual mind. This is why Descartes presents his revolutionary arguments in the form of Meditations, which are, after all, a mind's silent, interior communications with itself.
When we come to the most important and most difficult part of the First Critique, the "Deduction of the Pure Concepts of Understanding," or Transcendental Deduction, as it is commonly called, we shall see that Kant reaches all the way back to this beginning point of Descartes' argument, and, in effect, shows us the correct conclusions that can be extracted from the simple proposition, "I think."