To ask "What is man?" is to ask "What is experience?" for experience means that of which I am conscious. The facts of consciousness are the only facts that, to begin with, we are justified in asserting to exist. On the other hand, they are valid evidence for whatever is necessary to their own explanation, i.e. for whatever is logically involved in them. Now the most striking characteristic of humans, that in fact which marks them specially, as contrasted with other animals, is self-consciousness. The simplest mental act into which we can analyse the operations of the human mind—the act of sense-perception—is never merely a change, physical or psychical, but is the consciousness of a change.
