Thirdly, the action of the conscience is marked by necessity. And by this we are to understand something more than the simple uniformity in which all the psychical activity, except that of the choices of the will, is held under "fixed laws of thought and feeling." The necessity here affirmed is that unique necessity which distinguishes and marks intuitive or _a priori_ cognition, as of time, space, and causality. "Necessity" is justly conceded to be one of the criteria of these and other intuitional "first truths." It is not at the option of the human mind whether it will think the world under the relations of time and space, or events as occurring under the principle of causation. These are "forms of knowledge," knowledge of super-sensible realities, that come not at our choice but by an unavoidable insight. The primary and fundamental ethical distinction belongs to such rational intuition, and is marked by the peculiar necessity of intuitional action. As on occasion of knowing material bodies with three dimensions, or of changes in consciousness or in the outer world, with the fact of co-existence or succession and duration, the phenomenal sphere is necessarily transcended and time and space are necessarily discerned, so when we understand the manifold relations in which our lives are to be lived, in which we may use our personal powers, either in harmony with or in violation of our given adaptations, and with either great injury or rich good to others, in the same necessary way the conscience must discern the distinction of right and wrong and the reality of duty.