Let us now turn from the imperfect analysis which the _sensational_ school presents, to the speculations of the _idealist_. It will be seen that the hasty conclusions of the first gave a sort of basis for the strange results to which the second would conduct us.
Kant looked in vain for the idea of extension, or of space, where the philosophers had been seeking it, in the phenomena of sensation. He pronounced, therefore, that it was not derivable from experience, did not come to us from without, through any direct communication from the senses. Not finding this idea of space where the analytical psychologist had been searching for it, he drew it at once from the mind itself. He described it as a product of the _subject_ man, a _form of the sensibility_ with which he invests his own sensations.
We must first remark, that to this description of what perception really is, there lies the same objection that may be urged against the account of the sensationalist. A sensation clothed in space!--is this intelligible? is it by any means an account of the matter? To invest sensation with space, is it not as if we spoke of a _pleasure_ that was _square_, or of a _circular pain_?
So far, however, as this internal origin of the idea of space is concerned, the statement of Kant, though expressed in unusual terms, is not opposed to the general belief of mankind, or to our irresistible convictions. It may merely convey this meaning, that the mind has an immediate knowledge (drawn from the laws of its own cogitation) of space, or extension. But then, according to the universal and unalterable convictions of mankind, this idea of space, though it may be derived from the innate resources of the mind, is in fact the knowledge of an external reality--of an _objective_ truth. Kant decided otherwise. He pronounced this _form of the sensibility_ to be merely and only a mode of thought--that space had, in fact, no other existence, was solely a _subjective_ truth.
This one decision has been the cause of, or at least has served as the starting-point for a series of the wildest speculations that perhaps philosophy has to record. And this decision, how arbitrary!--how dogmatic!
It must be manifest, we think, to every intelligent person, that, granting we cannot demonstrate the _objective truth_ of the existence of space, it is equally impossible to prove its _subjective_ nature. We cannot conceive of space but as existing really around us. The metaphysician says we may be deceived. This universal and irresistible conviction--this fundamental law of human belief, may not be correspondent with absolute truth, may not be trustworthy. Granted that we _may_ be deceived, that there is footing here for his _scepticism_, he cannot proceed a step further, and show that we _are_ deceived. When, in his turn, he would assert, or dogmatise, he at all events is as open to our scepticism as we were to his. If a fundamental belief of this kind is not to be trusted, so neither can it be convicted of falsehood. We cannot launch ourselves out of our own nature; we _cannot test_ our own faculties of cognition. This could only be done by some superior intelligence who could survey apart the object and the percipient subject.