of bodily existence (which is at once excluded by the change of matter).  The identity of the person or the ego must be carefully distinguished from that of substance and of man.  It would not be impossible for the person to remain the same in a change of substances, in so far as the different beings (for instance, the souls of Epicurus and Gassendi) participated in the same self-consciousness; and, conversely, for a spirit to appear in two persons by losing the consciousness of its previous existence.  Consciousness is the sole condition of the self, or personal identity.—­The determinations of space and time are for the most part relations.  Our answers to the questions “When?” “How long?” “How large?” denote the distance of one point of time from another (e.g., the birth of Christ), the relation of one duration to another (of a revolution of the sun), the relation of one extension to another well-known one taken as a standard.  Many apparently positive ideas and words, as young and old, large and small, weak and strong, are in fact relative.  They imply merely the relation of a given duration of life, of a given size and strength, to that which has been adopted as a standard for the class of things in question.  A man of twenty is called young, but a horse of like age, old; and neither of these measures of time applies to stars or diamonds.  Moral relations, which are based on a comparison of man’s voluntary actions with one of the three moral laws, will be discussed below.

The inquiry now turns from the origin of ideas to their cognitive value or their validity, beginning (in the concluding chapters of the second book) with the accuracy of single ideas, and advancing (in Book iv., which is the most important in the whole work) to the truth of judgments.  An idea is real when it conforms to its archetype, whether this is a thing, real or possible, or an idea of some other thing; it is adequate when the conformity is complete.  The idea of a four-sided triangle or of brave cowardice is unreal or fantastical, since it is composed of incompatible elements, and the idea of a centaur, since it unites simple ideas in a way in which they do not occur in nature.  The layman’s ideas of law or of chemical substances are real, but inadequate, since they have a general resemblance to those of experts, and a basis in reality, but yet only imperfectly represent their archetypes.  Nay, further, our ideas of substances are all inadequate, not only when they are taken for representations of the inner essences of things (since we do not know these essences), but also when they are considered merely as collections of qualities.  The copy never includes all the qualities of the thing, the less so since the majority of these are powers, i.e., consist in relations to other objects, and since it is impossible, even in the case of a single body, to discover all the changes which it is fitted to impart to, or to receive from, other substances.  Ideas of modes and relations