Implicitly all this was already laid down in the original argument of this book. The author adds the present amplification of the argument, because he has found by experience that some readers have not read attentively enough. It is to be remembered, too, that the idea of perception, developed in this book, is not to be confused with the idea of external sense-perception which is but a special case of the former. The reader will gather from what has preceded, but even more from what will be expounded later, that everything is here taken as "percept" which sensuously or spiritually enters into man's experience, so long as it has not yet been seized upon by the actively constructed concept. No "senses," as we ordinarily understand the term, are necessary in order to have percepts of a psychical or spiritual kind. It may be urged that this extension of ordinary usage is illegitimate. But the extension is absolutely indispensable, unless we are to be prevented by the current sense of a word from enlarging our knowledge of certain realms of facts. If we use "percept" only as meaning "sense-percept," we shall never advance beyond sense-percepts to a concept fit for the purposes of knowledge. It is sometimes necessary to enlarge a concept in order that it may get its appropriate meaning within a narrower field. Again, it is at times necessary to add to the original content of a concept, in order that the original thought may be justified or, perhaps, readjusted. Thus we find it said here in this book: "An idea is nothing but an individualised concept." It has been objected that this is a solecism. But this terminology is necessary if we are to find out what an idea really is. How can we expect any progress in knowledge, if every one who finds himself compelled to readjust concepts, is to be met by the objection: "This is a solecism"? THE REALITY OF FREEDOM VIII THE FACTORS OF LIFE