At a time when he was more troubled by the arguments of sceptics than he was earlier or later, he wrote a curious work called Dreams of a Ghost-seer, Illustrated by the Dreams of Metaphysics
( 1766). The “ghost-seer” is Swedenborg, whose mystical system had been presented to the world in an enormous work, of which four copies were sold, three to unknown purchasers and one to Kant. Kant, half seriously and half in jest, suggests that Swedenborg’s system, which
-705-
he calls “fantastic,” is perhaps no more so than orthodox metaphysics. He is not, however, wholly contemptuous of Swedenborg. His mystical side, which existed though it did not much appear in his writings, admired Swedenborg, whom he calls “very sublime.”
Like everybody else at that time, he wrote a treatise on the sublime and the beautiful. Night is sublime, day is beautiful; the sea is sublime, the land is beautiful; man is sublime, woman is beautiful; and so on.
The Encyclopedia Britannica remarks that “as he never married, he kept the habits of his studious youth to old age.” I wonder whether the author of this article was a bachelor or a married man.
Kant most important book is The Critique of Pure Reason. ( 1st edition 1781; 2nd edition 1787.) The purpose of this work is to prove that, although none of our knowledge can transcend experience, it is nevertheless in part a priori and not inferred inductively from experience. The part of our knowledge which is a priori embraces, according to him, not only logic, but much that cannot be included in logic or deduced from it. He separates two distinctions which, in Leibniz, are confounded. On the one hand there is the distinction between “analytic” and “synthetic” propositions; on the other hand, the distinction between “a priori” and “empirical” propositions. Something must be said about each of these distinctions.
An “analytic” proposition is one in which the predicate is part of the subject; for instance, “a tall man is a man,” or “an equilateral triangle is a triangle.” Such propositions follow from the law of contradiction; to maintain that a tall man is not a man would be selfcontradictory. A “synthetic” proposition is one that is not analytic. All the propositions that we know only through experience are synthetic. We cannot, by a mere analysis of concepts, discover such truths as “Tuesday was a wet day” or “Napoleon was a great general.” But Kant, unlike Leibniz and all other previous philosophers, will not admit the converse, that all synthetic propositions are only known through experience. This brings us to the second of the above distinctions.
An “empirical” proposition is one which we cannot know except by the help of sense-perception, either our own or that of some one else whose testimony we accept. The facts of history and geography are of this sort; so are the laws of science, whenever our knowledge of their truth depends on observational data. An “a priori” proposi-
-706-
tion, on the other hand, is one which, though it may be elicited by experience, is seen, when known, to have a basis other than experience. A child learning arithmetic may be helped by experiencing two marbles and two other marbles, and observing that altogether he is experiencing four marbles. But when he has grasped the general proposition “two and two are four” he no longer requires confirmation by instances; the proposition has a certainty which induction can never give to a general law. All the propositions of pure mathematics are in this sense a priori.
Hume had proved that the law of causality is not analytic, and had inferred that we could not be certain of its truth. Kant accepted the view that it is synthetic, but nevertheless maintained that it is known a priori. He maintained that arithmetic and geometry are synthetic, but are likewise a priori. He was thus led to formulate his problem in these terms:
How are synthetic judgements a priori possible?
The answer to this question, with its consequences, constitutes the main theme of The Critique of Pure Reason.
Kant’s solution of the problem was one in which he felt great confidence. He had spent twelve years in looking for it, but took only a few months to write his whole long book after his theory had taken shape. In the preface to the first edition he says: “I venture to assert that there is not a single metaphysical problem which has not been solved, or for the solution of which the key at least has not been supplied.” In the preface to the second edition he compares himself to Copernicus, and says that he has effected a Copernican revolution in philosophy.
According to Kant, the outer world causes only the matter of sensation, but our own mental apparatus orders this matter in space and time, and supplies the concepts by means of which we understand experience. Things in themselves, which are the causes of our sensations, are unknowable; they are not in space or time, they are not substances, nor can they be described by any of those other general concepts which Kant calls “categories.” Space and time are subjective, they are part of our apparatus of perception. But just because of this, we can be sure that whatever we experience will exhibit the characteristics dealt with by geometry and the science of time. If you always wore blue spectacles, you could be sure of seeing everything blue
-707-
(this is not Kant’s illustration). Similarly, since you always wear spatial spectacles in your mind, you are sure of always seeing everything in space. Thus geometry is a priori in the sense that it must be true of everything experienced, but we have no reason to suppose that anything analogous is true of things in themselves, which we do not experience.
Space and time, Kant says, are not concepts; they are forms of “intuition.” (The German word is “Anschauung,” which means literally “looking at” or “view.” The word “intuition,” though the accepted translation is not altogether a satisfactory one.) There are also, however, a priori concepts; these are the twelve “categories,” which Kant derives from the forms of the syllogism. The twelve categories are divided into four sets of three: (1) of quantity: unity, plurality, totality; (2) of quality: reality, negation, limitation; (3) of relation: substance-and-accident, cause-and-effect, reciprocity; (4) of modality: possibility, existence, necessity. These are subjective in the same sense in which space and time are–that is to say, our mental constitution is such that they are applicable to whatever we experience, but there is no reason to suppose them applicable to things in themselves. As regards cause, however, there is an inconsistency, for things in themselves are regarded by Kant as causes of sensations, and free volitions are held by him to be causes of occurrences in space and time. This inconsistency is not an accidental oversight; it is an essential part of his system.
A large part of The Critique of Pure Reason is occupied in showing the fallacies that arise from applying space and time or the categories to things that are not experienced. When this is done, so Kant maintains, we find ourselves troubled by “antinomies”–that is to say, by mutually contradictory propositions each of which can apparently be proved. Kant gives four such antinomies, each consisting of thesis and antithesis.
In the first, the thesis says: “The world has a beginning in time, and is also limited as regards space.” The antithesis says: “The world has no beginning in time, and no limits in space; it is infinite as regards both time and space.”
The second antinomy proves that every composite substance both is, and is not, made up of simple parts.
The thesis of the third antinomy maintains that there are two kinds
-708-
of causality, one according to the laws of nature, the other that of freedom; the antithesis maintains that there is only causality according to the laws of nature.
The fourth antinomy proves that there is, and is not, an absolutely necessary Being.
This part of the Critique greatly influenced Hegel, whose dialectic proceeds wholly by way of antinomies.
In a famous section, Kant sets to work to demolish all the purely intellectual proofs of the existence of God. He makes it clear that he has other reasons for believing in God; these he was to set forth later in The Critique of Practical Reason. But for the time being his purpose is purely negative.
There are, he says, only three proofs of God’s existence by pure reason; these are the ontological proof, the cosmological proof, and the physico-theological proof.
The ontological proof, as he sets it forth, defines God as the ens realissimum, the most real being; i.e., the subject of all predicates that belong to being absolutely. It is contended, by those who believe the proof valid, that, since “existence” is such a predicate, this subject must have the predicate “existence,” i.e., must exist. Kant objects that existence is not a predicate. A hundred thalers that I merely imagine may, he says, have all the same predicates as a hundred real thalers.
The cosmological proof says: If anything exists, then an absolutely necessary Being
