§5 It is needful to guard against the grave error of supposing that because perception arises through the knowledge of causality, the relation of subject and object is that of cause and effect. For this relation subsists only between the immediate object and objects known indirectly, thus always between objects alone. It is this false supposition that has given rise to the foolish controversy about the reality of the outer world; a controversy in which dogmatism and scepticism oppose each other, and the former appears, now as realism, now as idealism. Realism treats the object as cause, and the subject as its effect. The idealism of Fichte reduces the object to the effect of the subject. Since however, and this cannot be too much emphasised, there is absolutely no relation according to the principle of sufficient reason between subject and object, neither of these views could be proved, and therefore scepticism attacked them both with success. Now, just as the law of causality precedes perception and experience as their condition, and therefore cannot (as Hume thought) be derived from them, so object and subject precede all knowledge, and hence the principle of sufficient reason in general, as its first condition; for this principle is merely the form of all objects, the whole nature and possibility of their existence as phenomena: but the object always presupposes the subject; and therefore between these two [pg 017] there can be no relation of reason and consequent. My essay on the principle of sufficient reason accomplishes just this: it explains the content of that principle as the essential form of every object—that is to say, as the universal nature of all objective existence, as something which pertains to the object as such; but the object as such always presupposes the subject as its necessary correlative; and therefore the subject remains always outside the province in which the principle of sufficient reason is valid. The controversy as to the reality of the outer world rests upon this false extension of the validity of the principle of sufficient reason to the subject also, and starting with this mistake it can never understand itself. On the one side realistic dogmatism, looking upon the idea as the effect of the object, desires to separate these two, idea and object, which are really one, and to assume a cause quite different from the idea, an object in itself, independent of the subject, a thing which is quite inconceivable; for even as object it presupposes subject, and so remains its idea. Opposed to this doctrine is scepticism, which makes the same false presupposition that in the idea we have only the effect, never the cause, therefore never real being; that we always know merely the action of the object. But this object, it supposes, may perhaps have no resemblance whatever to its effect, may indeed have been quite erroneously received as the cause, for the law of causality is first to be gathered from experience, and the reality of experience is then made to rest upon it. Thus both of these views are open to the correction, firstly, that object and idea are the same; secondly, that the true being of the object of perception is its action, that the reality of the thing consists in this, and the demand for an existence of the object outside the idea of the subject, and also for an essence of the actual thing different from its action, has absolutely no meaning, and is a contradiction: and that the knowledge of the nature of the effect of any [pg 018] perceived object, exhausts such an object itself, so far as it is object, i.e., idea, for beyond this there is nothing more to be known. So far then, the perceived world in space and time, which makes itself known as causation alone, is entirely real, and is throughout simply what it appears to be, and it appears wholly and without reserve as idea, bound together according to the law of causality. This is its empirical reality. On the other hand, all causality is in the understanding alone, and for the understanding. The whole actual, that is, active world is determined as such through the understanding, and apart from it is nothing. This, however, is not the only reason for altogether denying such a reality of the outer world as is taught by the dogmatist, who explains its reality as its independence of the subject. We also deny it, because no object apart from a subject can be conceived without contradiction. The whole world of objects is and remains idea, and therefore wholly and for ever determined by the subject; that is to say, it has transcendental ideality. But it is not therefore illusion or mere appearance; it presents itself as that which it is, idea, and indeed as a series of ideas of which the common bond is the principle of sufficient reason. It is according to its inmost meaning quite comprehensible to the healthy understanding, and speaks a language quite intelligible to it. To dispute about its reality can only occur to a mind perverted by over-subtilty, and such discussion always arises from a false application of the principle of sufficient reason, which binds all ideas together of whatever kind they may be, but by no means connects them with the subject, nor yet with a something which is neither subject nor object, but only the ground of the object; an absurdity, for only objects can be and always are the ground of objects. If we examine more closely the source of this question as to the reality of the outer world, we find that besides the false application of the principle of sufficient reason generally to what lies [pg 019] beyond its province, a special confusion of its forms is also involved; for that form which it has only in reference to concepts or abstract ideas, is applied to perceived ideas, real objects; and a ground of knowing is demanded of objects, whereas they can have nothing but a ground of being. Among the abstract ideas, the concepts united in the judgment, the principle of sufficient reason appears in such a way that each of these has its worth, its validity, and its whole existence, here called truth, simply and solely through the relation of the judgment to something outside of it, its ground of knowledge, to which there must consequently always be a return. Among real objects, ideas of perception, on the other hand, the principle of sufficient reason appears not as the principle of the ground of knowing, but of being, as the law of causality: every real object has paid its debt to it, inasmuch as it has come to be, i.e., has appeared as the effect of a cause. The demand for a ground of knowing has therefore here no application and no meaning, but belongs to quite another class of things. Thus the world of perception raises in the observer no question or doubt so long as he remains in contact with it: there is here neither error nor truth, for these are confined to the province of the abstract—the province of reflection. But here the world lies open for sense and understanding; presents itself with naive truth as that which it really is—ideas of perception which develop themselves according to the law of causality.