This suggestion of Kant's has been elaborated in many modern writers on philosophy, who have pointed out how much scientific method is governed by the notion of the most easily intelligible theory, and they have argued that science assumes, for the convenience of method, principles which it never completely proves. These principles are called sometimes methodological assumptions, sometimes postulates. The difference between such modern writers and Kant is that the former think that all a priori principles are of this nature, and that the principle of causation, for example, is itself only a postulate.

The faculty of judgment, then, according to Kant, assumes for regulative purposes that nature is purposive to our understanding. What does this last phrase mean? We are often concerned to know the relation of things to our purposes. It has been pointed out that very many of our empirical concepts represent rather our practical interest in things than our desire to understand them as they are. Kant's phrase implies that, apart from any such relation to particular purposes, there is a more general purpose of mere intelligibility, which some objects obviously serve more than others.

Here we pass to the consideration of art, for in our judgments of beauty Kant holds that we similarly disregard the relation of the beautiful object to any particular purpose, and seem to be concerned with general purposiveness. The judgment of beauty is, for Kant, the supreme act of the faculty of judgment. It is reflection on an individual for its own sake, without attempting to fit it to our desires or see it as an instance of our concepts or rules. Kant therefore proceeds to examine our judgments of beauty, which show how reflection on individual objects may display general rules, and then proceeds, in the last part of the Critique, to discuss the part played by the concept of purposiveness in our understanding of nature.

It would seem at first sight that Kant is not interested in art for its own sake, but for the light which it throws upon the nature of our intellectual faculties. Nevertheless he is careful to insist on the distinction between artistic and scientific judgments. The judgment of beauty, he insists, is free, is not determined by a concept. We are not concerned, in such judgments, with asking what an object is. In so far as, in our appreciation of beauty, we bring in such considerations we are wrong. He therefore rules out any theory that beauty is concerned with faithful representation. Beauty consists in the form of an object, and in nothing else. The judgment of beauty, besides being free, is also disinterested. The relation of the beautiful object to our purposes is irrelevant to its beauty. The judgment of beauty cannot, therefore, be determined by rules of any kind. It is always individual and immediate, and the immediate feeling of beauty counts for more than any rules or canons of taste. Kant therefore vindicates art as independent of either science or morality. Yet, once we realise its independence, the nature of art throws light upon both science and morality; for the judgment of beauty, although free and not determined by concepts, claims universal validity. We might put Kant's point in another way by saying that art is significant, and yet is not significant of anything in particular. Its meaning cannot be reduced to scientific statement nor abstracted from its form, and yet art has meaning. Kant finds the explanation of the fact that the judgment of beauty is free, and yet claims universal validity, in the suggestion that a beautiful object is one the contemplation of which arouses and enlivens the two faculties of the intelligence, the imagination and the understanding, in their proper proportion or harmony. All knowledge needs imagination, the power of seeing resemblances and differences in objects, and understanding which by concepts gives unity and rules to the imagination. In science the imagination is subordinate to the understanding, for the aim of science is definiteness and precision. In art the imagination is free, and yet art is not the mere seeing of resemblances and differences; it also has its unity. It aims at the best proportion of variety and unity. This is independent of the varying natures of individual persons, and therefore the judgment of beauty can claim to be universally valid.

Beautiful objects, then, are "purposive to the understanding," inasmuch as their form stimulates in the most harmonious degree the two faculties of intelligence, and in art we find proof that there is a principle of general intelligibility, which may guide the work of the scientist. The purpose of the scientist is quite different from that of the artist, but if he is to reduce his facts to order and intelligibility he must be guided by a principle which is seen in its pure form in the artist.

In the second place, an understanding of the nature of art has significance for moral theory, because the judgment of beauty is disinterested, and shows that pleasure may be independent of desire. In æsthetic pleasure we are not merely determined by our inclinations, for art is of all human activities free and creative. We enjoy art not because it serves any of our individual desires and purposes, it is enjoyed by something in us that is universal. Art, then, contradicts the position which Kant assumes in the second Critique, that we cannot follow pleasure without being slaves of our phenomenal nature. It is a disinterested enjoyment, and is witness to the possibility of disinterested pleasure in the good. Further, Kant held that in one kind of æsthetic enjoyment, appreciation of the sublime, the contrast between our weakness and the vast extent and overwhelming powers of nature, calls forth in us a conviction accompanied by pleasure of the yet greater might of the moral law within us. Art therefore may become the symbol of morality, and the third Critique does much to soften the rigour of the teaching of the second.

In the last part of the Critique of Judgment Kant applies his doctrine of regulative principles to the understanding of nature. The faculty of judgment, as we saw, is concerned with the attempt to give unity to the detail of the natural world. In this work it has two regulative principles, mechanism and teleology. Reality cannot be formed according to both these principles; for mechanism assumes that reality can be regarded as a pattern or complex of recurring or interchangeable parts whose changes are necessitated, teleology that the world cannot be explained without supposing purpose to be an operating agency in change. Mechanism seeks to explain things as the necessary result of their original condition, teleology in the light of their highest development. The two principles have therefore been held to be inconsistent. The scientist, jealous for the validity of his discovery of mechanism, combats the very notion of purposive agency. The theologian thinks that to admit mechanism anywhere is to give up his whole position.

Kant's solution of this antinomy is that both mechanism and teleology are only regulative principles. They tell us nothing of the ultimate nature of reality, except that we can explain much of it by regarding it as if it were a machine, and much by regarding it as if it were the field of purposive agency. Reality must be consistent with both these facts, but more we cannot say. The moral is that we should continue to treat them as regulative principles, and push each principle of explanation as far as it will go.

Kant is here, as usual, the enemy alike of scientific and of theological dogmatism. He will not allow any limit to be set to the work of scientific investigation, and yet will not allow a principle of scientific method to be converted from an explanation of perceived facts into a theory of the universe.

Besides mediating between the conflicting claims of mechanism and teleology, Kant also modifies the notion of teleology. When we think of reality as purposive, we do not necessarily think of it as having a definite purpose, as being subordinate, for example, to the well-being of man. The principle of purposiveness arises properly, he holds, from the contemplation of living things, from the perception of the difference between an organism and a machine. An organism is purposive in the sense in which a work of art is. In applying the principle we are trying to understand reality as though the relation of all the different things in it were like the relation of the parts of an organism or a picture. But this principle, like the principle of mechanism, does not carry us further than the facts we have examined, for an organism or a work of art can only be understood by study of the individual relations of all its parts. We can never know the universe as an organism, for we can never know all its parts. We can understand and put together more and more of them, but we never come to the end.