But in neither assumption is there anything to prevent the philosopher in question from studying the movements of the chess-men and the way in which at every move or moment they are redistributed. At first their movements would probably be rather bewildering; but in course of time he would note, we may assume, that Black never moved unless White had previously moved, and that any movement of White was followed by one on the part of Black. He might therefore be tempted to lay it down as a rule that Black never moved unless White moved first--that an effect never occurred without a cause; and that a movement of White was always followed by a move on the part of Black--that a cause was always followed by its effect. But if he yielded to this temptation he would be making an assumption, for--inasmuch as he professes to know nothing to begin with--he does not _know_ that the pieces always will move in this way; he only knows (assuming that memory is not a mere delusion, as it may be, for anything he knows) that they have moved thus, not that they always will move thus. He may, however, assume that they will continue to move in that way. But with every fresh assumption he becomes less and less of an agnostic. He may, indeed, if he likes, further assume, not only that the pieces will move in this way, but that they must. This assumption does not, indeed, seem necessary; for if we know (or assume that we know) that they will follow this course, it seems superfluous to say that they must. It seems well, therefore, to try to see on what principle we are to make our assumptions. It is an ancient rule, and one followed by science, to make as few as possible--that is to say, the fewest that will suffice for the purpose in hand. If, therefore, the purpose of our study of the chess-board is merely to find out how and according to what rules the pieces actually do move, have moved, and will move, it seems sufficient to assume that they will move as they have done, not that they must. If, on the other hand, we want to know why they move in the way that we assume them to move, then the assumption that they do so because they must is certainly in form legitimate, though it may or may not be the right one in fact. Some people refuse to discuss such questions as "Why this universe?" "What is the reason of this unintelligible world?" on the ground that they cannot be answered except by making assumptions which cannot be proved. But is that really a good reason for refusing? If it is, then none of the questions which science exists to answer can be discussed, for they also can only be answered by assuming, without proof or possibility of proof, that Nature is uniform, that the chess-men will continue to move as they have done.