Kant, Prolegomena to any Future Metaphysic

Returning to an example used earlier the synthetic

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Unformatted text preview: riori synthetic knowledge that is, at least, unchallenged; we don’t have to ask whether such knowledge is possible (for it is real), but only how it is possible. When we can answer that, we shall know how to go about showing the possibility of all other kinds of synthetic a priori knowledge. Section 5: The general problem: how can there be knowledge based on pure reason? We have seen the vast difference between analytic and synthetic judgments. It is easy to see how there can be analytic propositions: they come purely from the law of contradiction. There is also no special problem about how there can be synthetic propositions that are known a posteriori, that is, known from experience: experience itself is nothing but a continual joining together of perceptions, ·so it is not surprising that it enables us to join concepts in a synthetic way. Returning to an example used earlier, the synthetic proposition that some bodies are heavy can be established through experiences in which Ÿperceptions of body are joined with Ÿperceptions of weight·. What we do have a problem about is the possibility of synthetic propositions that are known a priori. Whatever makes this sort of knowledge possible, it is not the law of contradiction ·and it is not experience·, so we must search to find out what it is. But we cannot rightly start by asking whether synthetic a priori propositions are possible. For there are plenty of them, really given to us with undisputed certainty; and as our present procedure involves starting with what we already know, we shall start from the premise that there is human a priori knowledge of some synthetic propositions. But then we still have to ask how this knowledge is possible, that is, what makes it possible. When we know that, we can learn how to use such knowledge and can learn what its limits are. Stated precisely, then, the crucial question is this: How is it possible to have a priori knowledge of synthetic propositions? I have sometimes expressed this as a question about knowledge ‘out of pure reason’. That is just another way of asking the same thing. When I speak here of knowledge out of pure 16 reason, I always mean knowledge of synthetic propositions, never of analytic ones; ·and of course knowledge through pure reason is always a priori·. [At this point Kant has a footnote commenting on the shift from the old senses of ‘analytic’ and ‘synthetic’ (explained on page 7 above) to his new senses for those terms.] Metaphysics stands or falls with the solution to this problem. Someone may propound his metaphysical claims as plausibly as he likes, smothering us with conclusions piled on conclusions; but if he hasn’t first answered this question properly, we are entitled to say to him: ‘This is all pointless ungrounded philosophy and false wisdom. You purport to be using pure reason to create a priori knowledge, not by merely analysing concepts but by making new connections that don’t rest on the law of contradiction; and you think you have insight into these connections independently of all experience. But how do you get such insight? How can you justify your claims?’ He cannot answer by appealing to the common sense of mankind, for that is not evidence - it is mere hearsay. . . . The question must be answered, but that is difficult to do. One reason why an answer wasn’t attempted long ago is that a satisfactory answer to this one question demands much deeper, more persistent and more careful thought than goes into the most lengthy and ambitious metaphysical works ever published. (A weightier reason is that nobody thought to ask the question!) Every reader who looks hard at the problem will initially be frightened by its difficulty. Indeed, if it were not that there really is synthetic a priori knowledge, the thoughtful person would think such knowledge to be impossible. This is what happened to David Hume, although he didn’t put the question to himself in this general form (which is the form we need if we are to get an answer that is decisive for the whole of metaphysics). Hume asked an intelligent question: How can I arrive at a judgment in which one concept is connected necessarily with another, even though the one does not contain the other? He thought it couldn’t be done; which led him to conclude that only experience can provide us with such connections. In other words, he thought that this supposed necessity (which is the same as this supposed a priori knowledge) is merely a long-standing habit o f accepting something as true, and hence of taking Ÿa necessity in our thought - ·a mere mental compulsion· - to be Ÿa necessity in the world. If you want to complain about the toil and trouble that I am going to give you in solving this problem, I invite you to try solving it in an easier way! Perhaps that will make you grateful to the man who has taken this deep task over for you, and you may even come to be surprised - given how difficult the problem is - that the solution is not even harder than it is. I have had to work for many years to solve this problem in...
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This note was uploaded on 03/12/2013 for the course PHIL 105 taught by Professor Mendetta during the Spring '13 term at SUNY Stony Brook.

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