Phenomena of the external sense are examined and set forth in physics; those of the internal sense in empirical psychology. Pure mathematics consider… - Immanuel Kant

Let the letters a b c denote the three angular points of a rectilineal triangle. If the point did move continuously over the lines ab, bc, ca, that is, over the perimeter of the figure, it would be necessary for it to move at the point b in the direction ab, and also at the same point b in the direction bc. These motions being diverse, they cannot be simultaneous. There-fore, the moment of presence of the movable point at vertex b, considered as moving in the direction ab, is different from the moment of presence of the movable point at the same vertex b, considered as moving in the same direction bc. But between two moments there is time; therefore, the movable point is present at point b for some time, that is, it rests. Therefore it does not move continuously, which is contrary to the assumption. The same demonstration is valid for motion over any right lines including an assignable angle. Hence a body does not change its direction in continuous motion except by following a line no part of which is straight, that is, a curve, as Leibnitz maintained.

The concept of happiness is not one which man abstracts more or less from his instincts and so derives from his animal nature. It is, on the contrary, a mere idea of a state, and one to which he seeks to make his actual state of being adequate under purely empirical conditions — an impossible task. He projects this idea himself, and, thanks to his intellect, and its complicated relations with imagination and sense, projects it in such different ways, and even alters his concept so often, that were nature a complete slave to his elective will, it would nevertheless be utterly unable to adopt any definite, universal and fixed law by which to accommodate itself to this fluctuating concept and so bring itself into accord with the end that each individual arbitrarily sets before himself. But even if we sought to reduce this concept to the level of the true wants of nature in which our species is in complete and fundamental accord, or, trying the other alternative, sought to increase to the highest level man's skill in reaching his imagined ends, nevertheless what man means by happiness, and what in fact constitutes his peculiar ultimate physical end, as opposed to the end of freedom, would never be attained by him. For his own nature is not so constituted as to rest or be satisfied in any possession or enjoyment whatever. Also external nature is far from having made a particular favorite of man or from having preferred him to all other animals as the object of its beneficence. For we see that in its destructive operations — plague, famine, flood, cold, attacks from animals great and small, and all such things — it has as little spared him as any other animal. But, besides all this, the discord of inner natural tendencies betrays man into further misfortunes of his own invention, and reduces other members of his species, through the oppression of lordly power, the barbarism of wars, and the like, to such misery, while he himself does all he can to work ruin to his race, t

Handle so, daß du die Menschheit, sowol in deiner Person, als in der Person eines jeden andern, jederzeit zugleich als Zweck, niemals bloß als Mittel brauchest.