The supposition is, however, untrue. We relate percepts to ourselves not merely ideally, through concepts, but also, as we have already seen, through feeling. In short, the content of our lives is not merely conceptual. The Naïve Realist holds that the personality actually lives more genuinely in the life of feeling than in the purely ideal activity of knowledge. From his point of view he is quite right in interpreting the matter in this way. Feeling plays on the subjective side exactly the part which percepts play on the objective side. From the principle of Naïve Realism, that everything is real which can be perceived, it follows that feeling is the guarantee of the reality of one's own personality. Monism, however, must bestow on feeling the same supplementation which it considers necessary for percepts, if these are to stand to us for reality in its full nature. For Monism, feeling is an incomplete reality, which, in the form in which it first appears to us, lacks as yet its second factor, the concept or idea. This is why, in actual life, feelings, like percepts, appear prior to knowledge. At first, we have merely a feeling of existence; and it is only in the course of our gradual development, that we attain to the point at which the concept of Self emerges from within the blind mass of feelings which fills our existence. However, what for us does not appear until later, is from the first indissolubly bound up with our feelings. This is how the naïve man comes to believe that in feeling he grasps existence immediately, in knowledge only mediately. The development of the affective life, therefore, appears to him more important than anything else. Not until he has grasped the unity of the world through feeling will he believe that he has comprehended it. He attempts to make feeling rather than thought the instrument of knowledge. Now a feeling is entirely individual, something equivalent to a percept. Hence a philosophy of feeling makes a cosmic principle out of something which has significance only within my own personality. Anyone who holds this view attempts to infuse his own self into the whole world. What the Monist strives to grasp by means of concepts the philosopher of feeling tries to attain through feeling, and he looks on his own felt union with objects as more immediate than knowledge. The tendency just described, the philosophy of feeling, is Mysticism. The error in this view is that it seeks to possess by immediate experience what must be known, that it seeks to develop feeling, which is individual, into a universal principle. A feeling is a purely individual activity. It is the relation of the external world to the subject, in so far as this relation finds expression in a purely subjective experience.