We _may be_ deceived in believing that we ourselves exist--that there is any permanent being we call ourselves--but there is no demonstrating that we _are_ so deceived. The two cases are strictly analogous. We have just the same proof of the existence of the external object as of the thinking and percipient subject. The very first sensation or perception we experience brings with it instantaneously the two correlates, object and subject; they are made known in the same act or feeling; they are made known the one by means of the other--for unless through the means of the antagonist idea of object we should not have that of subject, nor _vice versâ_. In our judgment, therefore, there is as little philosophy in denying the external existence of matter as the internal existence of mind. The two ideas, as we have said, rise instantaneously, synchronously, and are in such manner correlates that it is only by the presence of the one that the other reveals itself.[6]
When Kant advanced from doubting of the _objective_ truth of our knowledge of space, to deciding against it--to asserting that it was purely _subjective_--he was exceeding the limits of the human faculties, and offering a mere dogmatism which can never be brought to any test whatever. He was asking us to judge of the trustworthiness of our faculties of cognition--by what?--by our faculties of cognition. He was elevating what is at best a strange suspicion, a mere _guess_, into a doctrine.
And the whole superstructure of the systems of idealism which his German followers have reared, rests upon this guess!
Kant left nothing of the material world but an indescribable _noumenon_, which did not even exist in space. Of course the categories of Aristotle, classifying as they did those relations which constitute our knowledge of this world, were converted by him into mere forms of the _understanding_, moulding the given products of the _sensibility_. Certain other regulative modes of thought predominating, in their turn, over the products of the _understanding_, he called ideas of the _pure reason_.
His successor, Fichte, it will be seen, advanced but little further when he pronounced for a system of _idealism_. The subjective nature of our knowledge had been laid down; there was nothing left of the real world but this _noumenon_ which had been ejected from the realm of space; he acted, therefore, a consistent and charitable part, in taking this forlorn and banished entity into the region, at least, of thought. All the external world is now but a projection from the individual mind--the _non-ego_ is but another development of the _ego_--the _object_ is nothing but a sort of limitation or contrast which the subject throws out, to make a life for itself; the web it spins in the blank infinitude. Of the whole material world we have for ever got rid.