perceptions, because at any moment they may cease to be his perceptions, and he receives or may receive different impressions. His perceptions are or may be incessantly changing; all his thoughts are or may be incessantly changing. In short, he is cognisant at first of nothing but change. He is inclined to generalise that observation, and to maintain that change is the essence of the universe. After a time, however, he considers, and he asks himself the question, But is there nothing but change? In other words, does the observer of the changes change just as much as the objects of his observation change? Is there at every moment a new observer as well as a new observed? This consideration causes the speculator to pause. No, says he, there is not, there cannot be a new observer for every new thing observed. If there were, no observation, no knowledge, no consciousness, could take place. The speculator sees that, if he, the observer, were changed into a different observer with every change that took place in his perception, that all thoughts, all cognition, all perception, would be rendered impossible and absurd. In other words, he sees that the wildest contradiction is involved in the supposition that every time the object is changed he (the subject, as we nowadays call it) is also changed; that a different he came into the field with every new presentation. And hence there is forced upon him this necessary thought, this thought which he cannot help thinking, and which we may divide into two thoughts: first, that change
