that of which it is the sign; and that is not the case. It follows, therefore, that none of those things which are not visible in themselves admit of being perceived; for one considers signs as things which aid in the perception of that which is not evident by itself.
They also wholly discard, and, as far as depends on them, overturn the idea of any cause, by means of this same train of reasoning. Cause is something relative. It is relative to that of which it is the cause. But that which is relative is only conceived, and has no real existence. The idea of a cause then is a pure conception; for, inasmuch as it is a cause, it must be a cause of something; otherwise it would be no cause at all. In the same way as a father cannot be a father, unless there exists some being in respect of whom one gives him the title of father; so too