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 



