I am only glossing the B version of the introduction–that is, the version of the introduction written by Kant for the second edition of the Critique. While I am sure the scholarship on the differences between the A and B versions is interesting, it is not my immediate interest.
SECTION I. THE DISTINCTION BETWEEN PURE AND EMPIRICAL KNOWLEDGE
Objects affect our senses and produce representations; these representations are compared and combined and separated (worked up) into knowledge of objects which we call experience. All knowledge begins with experience, but does not all arise from experience. It may well be that experience is only the occasion, the realizer, of knowledge–which already lies latent before experience in the human mind.
Is there knowledge that is independent of the experience, though? Such knowledge is called a priori, and is distinguished from the empirical, or a posteriori, or that which is known through experience. By a priori is not meant knowledge of a world, which is brought about through experience, but which is not yet experienced, e.g. knowledge that a house will collapse before it collapses. By a priori is meant knowledge that has no origin whatsoever in experience.
We are, in a word, interested in pure a priori knowledge. This can be contrasted to impure a priori knowledge, e.g. ‘every change has a cause.’ This is impure a priori knowledge, rather than pure a priori knowledge, because change is a concept which can only be found in experience.
SECTION II. WE ARE IN POSSESSION OF CERTAIN MODES OF A PRIORI KNOWLEDGE, AND EVEN THE COMMON UNDERSTANDING IS NEVER WITHOUT THEM
A priori judgments are both necessary and universal. Judgments from experience are neither. A judgment from experience says only that something is; it does not say whether or not it is necessary. Kant will later argue that the capacity to know if something is necessary or not comes from reason, not experience: science (at least nomothetic science [nomothetic= law-stating]), whose main subject matter finds its possibility a priori, is the foundation on which we can make any claim regarding necessity.
And a judgment from experience only has “assumed and comparative universality,” not strict universality as such. We can say that all swans are white on the basis of only seeing white swans, but this universality is only relative to our own experience. In order to make a truly universal judgment, then, we need to bring into play something apart from experience. This something is a priori knowledge. Making a priori knowledge the foundation for strictly universal judgments was Kant’s response to Hume’s and other similar objections to making universal statements on the basis of induction.
An example of such a necessary and universal statement: “every alteration must have a cause.” Kant claims that Hume’s attempt to derive it from a repeated association of experiences fails because what is produced is merely a subjective necessity.
COMMENTARY: But would this be a problem, if this subjective necessity were replicated in the experience of many, and then transformed into speech, making it possible to corroborate this “subjective necessity”–thereby producing an objective knowledge?
Kant then makes an important argument: “Even without appealing to such examples, it is possible to show that pure a priori principles are indispensable for the possibility of experience, and to so prove their existence a priori. For whence could experience derive its certainty, if all the rules, according to which it proceeds, were always themselves empirical and therefore contingent?”
COMMENTARY: But what rules does Kant mean? Does Kant mean the rule of turning experience into necessary and universal judgments? But does the common person ever really make necessary and universal judgments in the philosophical sense? That is to say, is the function of speech of the common person when he says, “All roses are red,” to make a scientific statement (a necessary and universal one), or rather, is it not to limit the possibility of action? Perhaps the common man says that all roses are red not PRIMARILY to make a universal statement, but instead to discourage his friend from looking for white roses. So while the propositional content of the statement, its context specific content and the way it is said are perhaps the real point of the statement, e.g. “All roses are RED!” Is it possible, therefore, that to focus on the epistemological content of the proposition is to miss the point of the proposition in common experience? Who is to say, moreover, that when we say that “all roses are red,” we really mean what we experience? For Kant means to suggest just that–that what we experience can only be made possible by these sorts of a priori judgments. But what if judgments are not essential to experience as such, but only extraneous? It may be necessary to wait to see what Kant means by experience.
Kant makes a final argument based on Aristotelian metaphysics, which he claims is an appeal to common sense. If we subtract all properties from an object, we are still left with the substance (being, or in Greek ousia) of the object, and this cannot be taken away. “Owing, therefore, to the necessity with which this concept of substance forces itself upon us, we have no option save to admit that it has its seat in our faculty of a priori reason.” I for one am not convinced on this point. More on this in next section.
SECTION III. PHILOSOPHY STANDS IN NEED OF A SCIENCE WHICH SHALL DETERMINE THE POSSIBILITY, THE PRINCIPLES, AND THE EXTENT OF ALL A PRIORI KNOWLEDGE
Kant opens with the following sentence:
“But what is still more extraordinary than all the preceding is this, that certain modes of knowledge leave the field of all possible experiences and have the appearance of extending the scope of our judgments beyond all limits of experience, and this by means of concepts to which no corresponding object can ever be given in experience.”
COMMENTARY: Isn’t that precisely what the concept of substance does? I leave this an open question.
Kant gives us the same story we have been given in the prefaces. Reason is endlessly motivated to find solutions to the nature of God, freedom, and immortality; the result is metaphysics. With metaphysics, the most reasonable thing would be to carefully determine whether the foundations for metaphysics are legitimate. But this, according to Kant, rarely happens in reality. Instead, as with Plato, metaphysics is constructed in the empty space of pure understanding–so easy, because the space offers no resistance, but impoverished because the space offers no resistance to the wings of thought and therefore no reality apart from fabrication through which to navigate.
Now what sustains this flight is the flattery of the “analysis of the concepts we already have of objects.” And “this analysis supplies us with a considerable body of knowledge, which, while nothing but explanation or elucidation of what has already been thought in our concepts, though in a confused manner, is yet prized as being, at least as regards its form, new insight.” While this procedure yields real knowledge a priori, another process also takes place, whereby reason “introduces assertions of an entirely different order, in which it attaches to given concepts others completely foreign to them.” The distinction between these two processes must be made, and it is the topic of the following section.
SECTION IV. THE DISTINCTION BETWEEN ANALYTIC AND SYNTHETIC JUDGMENTS