granted that he is unable to notice even strong variations.  It is clear that this uncertainty which disturbs the whole trade cannot be eliminated as long as the psychological background has not been systematically studied.  Mere talking about the attention of the customer, and his ability to decide and select, and of his observations and his habits in the spirit of popular common-sense psychology, can never secure exact standards and definite demarcation lines.  The question is important not only where imitations of morally doubtful character are in the market.  Even the most honest manufacturer is in a certain sense obliged to imitate his predecessors, as they have directed the taste and habits of the public in particular directions, and as the product of his company would suffer unnecessarily if he were to disregard this psychical attitude of the prospective customers.  The economic legal situation accordingly suggests the question whether it would not be possible to devise methods for an exact measurement of the permissible similarity, and this demand for exactitude naturally points to the methods of the psychological experiment.  E.S.  Rogers, Esq., of Chicago, who has thoroughly discussed the legal aspect of the problem,[53] first turned my attention to the psychological difficulty involved.

When I approached the question in the Harvard psychological laboratory, it was clear to me that the degree of attention and carefulness which the court may presuppose on the part of the customer can never be determined by the psychologist and his experimental methods.  It would be meaningless, if we tried to discover by experiments a particular degree of similarity which every one ought to recognize or a particular degree of attention which would be sufficient for protection against fraud.  Such degrees must always remain dependent upon arbitrary decision.  They are not settled by natural conditions, but are entirely dependent upon social agreement.  A decision outside of the realm of psychology must fix upon a particular degree in the scale of various similarity values as the limit which is not to be passed.  The aim of the psychologist can be only to construct such a scale by which decisions may be made comparable and by which standards may become possible.  The experiment cannot deduce from the study of mental phenomena what degrees of similarity ought to be still admissible, but it may be able to develop methods by which different degrees of similarity can be discriminated and by which a certain similarity value once selected can always be found again with objective certainty.  After many fruitless efforts I settled on the following form of experiments, which I hope may bring us nearer to the attainment of the purpose.