4 r >8 POPULAR SCIENCE MONTHLY
but this is a radically different question from the one specifically stated at the outset. Thus the master himself clearly slipped from one mean- ing to the other; and we may be quite certain that some of the answers of his students were intended for one interpretation of the question and some for the other. I feel quite sure that no member of Professor Miinsterberg's class really thinks, when he looks up at the full moon, that a solid disk of the size of a carriage-wheel held up at arm's length would just suffice to shut it out from his view. He knows very well that that would shut out a considerable part of the whole sky; and the man who gave " a carriage-wheel " as his answer was almost certainly speaking of how large the moon seemed to him and not of the other question.
This example, from its peculiar nature, has required much space for its discussion; and I hasten to add that, in singling it out, I have put Professor Miinsterberg's worst foot foremost. In no other of the instances is there involved, as in this one, a fundamental error. Yet a defect which, in this instance, reached the proportions of downright error is in some measure present in nearly the whole of the article. The defect I have reference to is a failure adequately to discriminate between conscious inference or conjecture, on the one hand, and the immediate dictum of sense-perception, on the other. I am perfectly aware — and it is a commonplace not only of books on logic and psy- chology, but also of the ordinary text-books of law — that no sharp line can be drawn between these two things. In almost every judgment, however immediately it seems to be given by the impressions made on our senses, an element of inference, conscious or unconscious, enters. Yet there is a vast difference between different cases; and, furthermore, a difference which is distinctly recognized by the wayfaring man. Professor Miinsterberg begins his article by citing contradictions of testimony as to whether a road was dry or muddy and as to whether a man had a beard or not; but the staple of his article relates to esti- mates of the number of spots irregularly scattered on a sheet of card- board, the rapidity with which a pointer moves around a circular dial, the interval of time between two clicks, and the like. Nowhere does he intimate that there is any vital difference between questions like these and questions of the simpler kind with which he starts out. But when a man is asked how many people he sees in a hall or how fast a train is moving, he knows perfectly well that the validity of his answer is of a wholly different nature from that which attaches to his state- ment as to whether the road in front of him is wet or dry, or whether a man he is looking at has or has not a beard. In the former cases, he is guessing or consciously estimating, and knows he is guessing or consciously estimating ; but when he says that the road in front of him is wet or that the man he is looking at has a beard, he is making an assertion in which he places implicit reliance as the direct result of the