rent places at the
same time and for two things to be at the same time in the same place,
everything that at a given instant is in a given place is identical with
itself, and, on the other hand, distinct from everything else (no matter
how great the resemblance between them) that at the same moment exists in
another place. Space and time therefore form the _principium
individuationis_. By what marks, however, may we recognize the identity of
an individual at different times and in different places? The identity of
inorganic matter depends on the continuity of the mass of atoms which
compose it; that of living beings upon the permanent organization of
their parts (different bodies are united into _one_ animal by a common
life); personal identity consists in the unity of self-consciousness, not
in the continuity 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