Preface, Preamble and the General Question

Preface

These Prolegomena are not for the use of pupils, but of future teachers; and even for them they are not meant to help in arranging the exposition of an already existing science, but to help them discover this science itself.

My intention is to convince all those who find it worthwhile to occupy themselves with metaphysics that it is absolutely necessary to suspend their work for the present, to consider everything that has happened until now as not having happened, and before all else to raise the question: whether such a thing as metaphysics is even possible at all.

If it is a science, how does it happen that it cannot, like other sciences, obtain universal and lasting acclaim? If it is not a science, how does it happen that it continually puffs itself up under the semblance of a science, and holds the human understanding in suspense with hopes that are never extinguished but never fulfilled? It seems almost laughable that, while every other science makes continuous progress, metaphysics, which claims to be wisdom itself, whose oracle everyone consults, should constantly revolve on the same spot without advancing a single step.

Since the essays of Locke and Leibniz, or rather since the beginning of metaphysics so far as its history reaches, no event has occurred that could have been more decisive for the fate of this science than the attack made upon it by David Hume. He started chiefly from a single but important concept of metaphysics, namely, that of the connection of cause and effect. He challenged reason, which pretends to have generated this concept in her bosom, to answer him by what right she thinks that something can be so constituted that, if it is posited, something else must necessarily also be posited. He proved irrefutably that it is wholly impossible for reason to think such a connection a priori and from concepts. He concluded that reason deceives herself with this concept, taking it falsely for her own child, whereas it is nothing but a bastard of the imagination, impregnated by experience, which has brought certain representations under the law of association, and passes off the resulting subjective necessity — habit — for an objective necessity from insight.

Hume's argument is in his "Treatise of Human Nature" (1739–40) and "Enquiry concerning Human Understanding" (1748).

Hume struck a spark from which a light might well have been kindled, if it had caught some inflammable tinder, and if its glow had been carefully kept up and increased. But fate, which has always been unfavourable to metaphysics, would have it that he was understood by no one. One cannot without a certain pain observe how utterly his opponents, Reid, Oswald, Beattie, and lastly Priestley, missed the point of his problem.

They appealed to common sense. To appeal to common sense when insight and science fail, and not before — this is one of the subtle discoveries of recent times, by which the shallowest windbag can confidently take on the most profound thinker and hold his own with him. Seen in the light of day, it is nothing but an appeal to the judgement of the multitude, an applause at which the philosopher blushes, and the popular wag triumphs and grows insolent.

I freely admit: it was the remembrance of David Hume that, many years ago, first interrupted my dogmatic slumber, and gave my investigations in the field of speculative philosophy a quite new direction.

The most famous sentence of the "Prolegomena."

I tried first whether Hume's objection could not be put into a universal form, and soon found that the concept of the connection of cause and effect was by no means the only one by which the understanding thinks connections of things a priori, but that metaphysics consists altogether of such concepts. I sought to make sure of their number; and when I had succeeded in this, from a single principle, I proceeded to the deduction of these concepts, which I was now assured were not derived from experience, as Hume had feared, but had sprung from the pure understanding. This deduction was the most difficult thing that could ever be undertaken on behalf of metaphysics.

Kant then speaks of the obscurity of his Critique: it is dry, it is obscure, it is long. But not everyone can write like Hume, so subtly and so gracefully, or like Moses Mendelssohn, so soundly. The present work is a plan, after which the Critique itself may be read.

Preamble: Metaphysical Cognition

The sources of metaphysical cognition cannot be empirical. Its principles must never be taken from experience; for it is not to be physical but metaphysical cognition, namely cognition lying beyond experience.

All judgements are either analytic — merely explicative, adding nothing to the content of the cognition — or synthetic, ampliative, adding to it. "All bodies are extended" is analytic; "Some bodies are heavy" is synthetic. Judgements of experience are always synthetic. Mathematical judgements are all synthetic. And metaphysical judgements, properly so called, are all synthetic.

Kant notes that Hume himself took mathematics to be analytic; had he seen that it was synthetic a priori, Kant thinks, he would never have extended his scepticism so far — for his good sense would have saved him from attacking mathematics.

The General Question: Is Metaphysics Possible At All?

If a metaphysics that could assert itself as science were actual, if one could say, "Here is metaphysics; you need only learn it, and it will convince you irresistibly and unchangeably of its truth," then this question would be unnecessary. But it is not so. One cannot point to a single book, as one points to a Euclid, and say: this is metaphysics.

But we can begin with sciences that do exist, and that contain synthetic cognition a priori: pure mathematics and pure natural science. Their actuality is not in doubt; we need only ask how they are possible, and from there proceed to metaphysics.

So the main question of transcendental philosophy, how are synthetic propositions a priori possible, is divided into four questions: How is pure mathematics possible? How is pure natural science possible? How is metaphysics in general possible? How is metaphysics as science possible?