127. This is why the principle of contradiction requires the condition of time. The objects which we perceive are changeable; there is nothing either in their nature or in their modifications which involves existence. If they are, they may cease to be; and if this change does not constantly occur in their substance, it does in their accidents. Therefore we cannot affirm the absolute, but only the conditional contradiction of their being and not-being; it exists only on the supposition of simultaneousness.
128. If we conceived only necessary being, we could have no idea of time: its existence absolutely excludes its non-existence, and therefore the contradiction would be always absolute, never conditional.
129. A most important consequence results from this analysis. The perception of time with us implies the perception of the non-necessity of things. When we perceive a being which is not necessary, we perceive a being which may cease to be, in which case we have the idea of succession, of real or possible time. Here another reflection arises which is also important: the idea of time is the idea of contingency: the consciousness of time is the consciousness of our weakness.
130. The idea of time is so deep in our mind, that without it we could not form the idea of the me. The consciousness of the identity of the me supposes a link[34] which it is impossible to find without memory. Memory necessarily involves the relation of past, and, consequently, the idea of time.
[CHAPTER XVIII.]
SUMMING UP.
Let us collect together the doctrines of the preceding chapters.
131. Time is a question difficult to explain. Whoever denies this difficulty shows that he has meditated but superficially on the matter.
132. Motion is measured by time; but it is not a sufficient definition of time to call it the measure of motion.