I have previously reduced the whole science of logic to two facts. The first is that our perceptions being every thing for us, we are perfectly, completely, and necessarily sure of whatever we actually feel. The second is that consequently none of our judgments, separately taken, can be erroneous: inasmuch as we see one idea in another it is actually there; but their falsity, when it takes place, is purely relative to anterior judgments, which we permit to subsist; and it consists in this, that we believe the idea in which we perceive a new element to be the same as that we have always had under the same sign, when it is really different, since the new element which we actually see there is incompatible with some of those which we have previously seen; so that to avoid contradiction we must either take away the former or not admit the latter.