Prefaces and Introduction: The Question of Metaphysics

Preface to the First Edition (1781)

Human reason has this peculiar fate in one species of its cognitions: that it is burdened with questions which it cannot dismiss, since they are given to it as problems by the nature of reason itself; but which it also cannot answer, since they transcend every capacity of human reason.

Reason begins with principles whose use is unavoidable in the course of experience. With them it rises ever higher, to more remote conditions. But it soon becomes aware that in this way its work must remain forever incomplete, because the questions never cease; and so it finds itself compelled to resort to principles that go beyond all possible use in experience. In this way it falls into obscurity and contradictions. The battlefield of these endless controversies is called metaphysics.

There was a time when metaphysics was called the queen of all the sciences. Now, in accordance with the fashion of the age, she is despised on all sides; and the matron, outcast and forsaken, mourns like Hecuba: "Greatest of all, by force of so many sons and daughters — now I am dragged away, exiled, powerless."

Kant quotes Ovid's "Metamorphoses" on Hecuba, the queen of Troy, enslaved after its fall.

Our age is the genuine age of criticism, to which everything must submit. Religion through its holiness, and legislation through its majesty, commonly seek to exempt themselves from it. But then they arouse just suspicion against themselves, and cannot lay claim to that unfeigned respect which reason grants only to that which has been able to withstand its free and public examination.

This critique is a call to reason to undertake anew the most difficult of all its tasks, namely, that of self-knowledge; and to institute a court of justice, by which reason may secure its rightful claims while dismissing all groundless pretensions — not by mere decrees, but according to its own eternal and unchangeable laws. This court is no other than the critique of pure reason itself.

"Critique" (Kritik) means not attack, but examination: the testing of the powers and limits of reason by reason itself.

Preface to the Second Edition (1787)

Logic, since the time of Aristotle, has not had to take a single step backwards; and, what is remarkable, it has also been unable to take a single step forward, and so seems to all appearance finished and complete. Mathematics, since the Greeks, and natural science, since Galileo and Torricelli, have entered on the secure path of a science. When Galileo let his balls of a weight chosen by himself roll down an inclined plane, a light dawned on all students of nature. They comprehended that reason has insight only into what it itself produces according to its own design; that it must take the lead with principles for its judgements according to constant laws, and compel nature to answer its questions — not like a pupil who has recited to him whatever the teacher wants, but like an appointed judge who compels witnesses to answer the questions he puts to them.

Metaphysics has not yet been so fortunate. Let us therefore try whether we do not get further with the problems of metaphysics by assuming that objects must conform to our cognition. This would agree better with the possibility of an a priori cognition of them, which is to establish something about objects before they are given to us. This is just like the first thoughts of Copernicus, who, when he did not make good progress in the explanation of the celestial motions if he assumed that the entire host of stars revolved around the observer, tried whether he might not have greater success if he made the observer revolve and left the stars at rest.

This is Kant's famous "Copernican revolution" in philosophy: instead of assuming that our knowledge must conform to objects, he assumes that objects, as we can know them, must conform to the forms of our knowing.

But from this follows a remarkable result: that we can never get beyond the limits of possible experience; that we know things only as they appear to us, not as they are in themselves. And yet this very limitation is a gain. For if things in themselves were known by the same laws as appearances, then everything — including our own will — would be bound by the mechanism of nature, and freedom would be impossible. But if the same thing is regarded as appearance and as thing in itself, then the same will can be thought, in its appearance, as bound by natural law, and, as a thing in itself, as free.

I had therefore to deny knowledge in order to make room for faith.

"Ich mußte also das Wissen aufheben, um zum Glauben Platz zu bekommen" — the most quoted sentence of the second Preface. "Faith" here means rational moral faith in God, freedom and immortality, not religious dogma.

Introduction

There can be no doubt that all our cognition begins with experience. But though all our cognition begins with experience, it does not on that account all arise from experience.

It is quite possible that even our empirical cognition is a composite of that which we receive through impressions, and that which our own faculty of cognition supplies from itself. Cognition that is independent of all experience, and even of all impressions of the senses, is called a priori; that which has its sources in experience, a posteriori.

"A priori": before, or independent of, experience; "a posteriori": after, or derived from, experience.

Judgements are either analytic or synthetic. In analytic judgements, the predicate belongs to the subject as something already contained, covertly, in its concept: "All bodies are extended." I do not need to go beyond the concept of body to find extension in it. In synthetic judgements, the predicate lies wholly outside the concept, though it stands in connection with it: "All bodies are heavy." Analytic judgements only clarify; synthetic judgements extend our knowledge.

Judgements of experience are all synthetic. But there are also synthetic judgements a priori. All mathematical judgements are of this kind. One might think at first that the proposition 7 + 5 = 12 is merely analytic. But the concept of the sum of 7 and 5 contains nothing more than their union into a single number, and in it is not at all thought what this single number is that comprehends both. I must go beyond these concepts, calling to my aid the intuition of my five fingers, or of five points, and add the units of five, one by one, to the concept of seven. So the proposition is synthetic. Natural science, too, contains synthetic a priori judgements — that in all changes of the material world the quantity of matter remains unchanged; that in all communication of motion, action and reaction must always be equal. And metaphysics, at least in its aim, consists of nothing but synthetic a priori judgements: that the world must have a first beginning, and the like.

The real problem of pure reason is therefore contained in the question: How are synthetic judgements a priori possible?

This is the central question of the book. Hume had argued that our idea of necessary connection — of cause and effect — comes only from habit. Kant, who wrote in his "Prolegomena" (1783) that Hume had woken him from his "dogmatic slumber," sets out to show that some necessary truths about the world can be known a priori, but only of the world as it appears.

There are two stems of human cognition, which perhaps spring from a common but to us unknown root: namely, sensibility and understanding. Through the first, objects are given to us; through the second, they are thought.