Immanuel Kant's Critique of Pure Reason — trans. F. Max Müller

All external phenomena are such that their existence cannot be perceived immediately, but that we can only infer them as the cause of given perceptions : —

Therefore the existence of all objects of the external senses is doubtful. This uncertainty I call the ideality of external phenomena, and the doctrine of that ideality is called idealism ; in comparison with which the other doctrine, which maintains a possible certainty of the objects of the external senses, is called dualism.

Criticism of the Fourth Paralogisin of Transcendental

Psychology

We shall first have to examine the premisses. We are perfectly justified in maintaining that that only which is within ourselves can be perceived immediately, and that my own existence only can be the object of a mere perception. The existence of a real object therefore outside me

Transcendental Dialectic . 299

(taking this word in its intellectual meaning) can never be given directly in perception, but can only be added in thought to the perception, which is a modification of the internal sense, and thus inferred as its external cause. Hence Cartesius was quite right in limiting all perception, in the narrowest sense, to the proposition, I (as a thinking being) am. For it must be clear that, as what [p. 368] is without is not within me, I cannot find it in my apperception ; nor hence in any perception which is in reality a determination of apperception only.

In the true sense of the word, therefore, I can never perceive external things, but only from my own internal perception infer their existence, taking the perception as an effect of which something external must be the proximate cause. An inference, however, from a given effect to a definite cause is always uncertain, because the effect may be due to more than one cause. Therefore in referring a perception to its cause, it always remains doubtful whether that cause be internal or external ; whether in fact all so-called external perceptions are not a mere play of our external sense, or point to real external objects as their cause. At all events the existence of the latter is inferential only, and liable to all the dangers of inferences, while the object of the internal sense (I myself with all my representations) is perceived immediately, and its existence cannot be questioned.

It must not be supposed, therefore, that an idealist is he who denies the existence of external objects of the senses ; all he does is to deny that it is known by immediate perception, and to infer that we can never [p. 369] become perfectly certain of their reality by any experience whatsoever.

300 Transcendental Dialectic

Before I expose the deceptive illusion of our paralogism, let me remark that we must necessarily distinguish two kinds of idealism, the transcendental and the empirical.

Tra7iscendental idealism teaches that all phenomena are representations only, not things by themselves, and that space and time therefore are only sensuous forms of our intuition, not determinations given independently by themselves or conditions of objects, as things by themselves. Opposed to this transcendental idealism, is a transcendental realism, which considers space and time as something in itself (independent of our sensibility).

Thus the transcendental realist represents all external phenomena (admitting their reality) as things by themselves, existing independently of us and our sensibility, and therefore existing outside us also, if regarded according to pure concepts of the understanding.

It is this transcendental realist who afterwards acts the empirical idealist, and who, after wrongly supposing that the objects of the senses, if they are to be external, must have an existence by themselves, and without our senses, yet from this point of view considers all our sensuous representations insufficient to render certain the reality of their objects.