[From this point on, I am going to have to assume a certain degree of familiarity with Kant's theoretical philosophy on the part of my readers. It took me an entire book to say what I needed to say about that subject -- Kant's Theory of Mental Activity, Harvard University Press, 1963 -- and there is no way that I can even summarize the central points here.]
Kant's goal in the Critique is to establish the validity of two of the four great bodies of theoretical knowledge with which he was familiar: the mathematics of Euclid and the physics of Newton. The logic of Aristotle, he believed, required no such justification, because its claims, although both universal and necessary, are empty, or as mathematicians are wont to say, trivial. The fourth body of theoretical knowledge, the metaphysics of Leibniz, Kant argued, could not be established at all, and indeed, strictly speaking, is not true [although Kant himself vacillates on this point.] The universality and necessity of Euclidean geometry and Newtonian physics, Kant concluded, are purchased at the very heavy price of restricting the scope of their propositions to things as they appear to us in space and time, rather than as they are in themselves. He was prepared to accept this limitation on their validity because he believed that nothing was lost thereby that was needed for the progress of science.
But when it came to the fundamental principles of Morality, Kant would consider no such limitation on the absolute universality of the scope of its claims. To put the point in the technical jargon that he introduced or adapted to his purposes, mathematics and science assert claims that are both synthetic in their logical structure [unlike the claims of logic, which are analytic] and are known a priori, which is possible only because of their limitation to the realm of Appearance. [Recall that the terms a priori and a posteriori are adverbial, and modify such verbs as "to know" or "to assert," whereas the terms synthetic and analytic are adjectival, and modify nouns such as "proposition" and "judgment.] Morality also asserts claims that are synthetic and are yet knowable a priori, without however in any way being limited in their scope to the realm of Appearances.
We may wonder how Kant hopes to be able to establish so powerful and uncompromising a claim. We may indeed!
Among the many schools of thought on matters ethical, there are two schools, or traditions, prominent in his day that Kant took as particular targets of his criticism: Utilitarianism, and the Moral Sentiment School. Both had very ancient progenitors, but in Kant's day -- which is to say in the middle and later eighteenth century -- both schools found their strongest proponents in the British Isles. Utilitarianism, of course, had been given its canonical expression by Jeremy Bentham, whose Principles of Morals and Legislation appeared in 1781, the year in which Kant published the first edition o the Critique. The Moral Sentiment school was the joint product of a number of Scottish and English philosophers, among them Francis Hutcheson, Adam Smith, and David Hume.
From Kant's point of view, the fatal flaw in both Utilitarianism and the Theory of Moral Sentiments is that they ground their arguments on facts of human nature that are accidental, so to speak. It is a mere fact of the human constitution that we seek pleasure and shun pain. It is equally a mere fact of our constitution that we feel certain sentiments of approbation when presented -- in Hume's felicitous phrasing -- with actions or traits of character that are "useful or agreeable to ourselves or others." Were we constituted differently, as indeed we might have been, then our moral judgments, our approvals and disapprovals, would themselves differ, and this, Kant firmly believed, is utterly unacceptable. To say that my obligation to tell the truth or to keep my promises is merely a consequence of the way in which I and other human beings happen to be, Kant insisted, is the death of morality. Only principles of obligation that are completely independent of the facts of human nature can possibly ground morality.
But the First Principles of Practical Reason, as Kant would call them, are not trivial tautologies. It does not follow merely from the meaning of the verb "to lie" that it is everywhere and always wrong to lie. Nor can we find, in the mere concept of a promise, my obligation to keep my promises. When we turn to the central text of Kant's ethical writings, the Groundwork of the Metaphysics of Morals, we shall find him struggling with the problem of devising a demonstration of the absolute, unconditioned, universal validity of the Fundamental Principle of Morality.
It will probably come as no surprise to you to learn that Kant was raised in an extremely rigoristic, individualistic form of Protestantism known as Pietism. Although he would, in the latter part of the First Critique, put paid to the two thousand year old search for demonstrable knowledge of a divinity -- the branch of philosophy known as Rational Theology -- Kant remained true to the core moral teachings of his upbringing. In the Grundlegung, we shall see how he attempts to provide as much of a demonstration as he thinks is philosophically possible for the principles of morality that he learned as a boy.
Now, with Kant, there is always a great deal more going on than even the most compressed summary can adumbrate. Along with everything else he was concerned with, Kant engaged early with an ancient philosophical conundrum, the apparent conflict between Free Will and Determinism. On the one hand, we believe ourselves to be capable of choosing freely among alternative actions presented to us by experience, and it is because of that freedom, we believe, that we are morally responsible for our actions and can be held accountable for what we have done. On the other hand, our actions take place in the spatio-temporal world, in which -- or so science tells us -- everything that happens has a sufficient cause and hence is determined to take place as it does. Since it is in this realm of Appearance that we speak truth or falsehood, make promises, or act so as to help or harm others, it would appear, contrary to any supposition of freedom, that what we do is determined to happen as it does.
In the First Critique, Kant lays out a particularly rigorous and unforgiving version of causal determinism. As he argues in the Second Analogy, to be an event in the realm of Appearances just is to have objective time location, and to have objective time location just is to stand in a chain of causes and effects that stretches back to the beginning of time and forward to the end of time. There would appear to be no wiggle room there for a freely acting and hence morally responsible self.
But very early in the development of his mature philosophy, Kant saw what he believed to be a way out of this thicket. The very same limitation that he placed on the claims of science in the realm of Appearances, he believed, would open up a conceptual space in which he could demonstrate the existence of freedom and moral responsibility. A good deal farther along in this tutorial, we shall see exactly how he proposes to demonstrate the compatibility of Free Will and Determinism.
That, I think, is enough to get us started. Now we shall have to wait a week until I reclaim my personal copy of the Grundlegung in Paris.