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. 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 versa_. 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!