Whether the one or the other method is to be preferred must depend upon the nature of the particular commercial or industrial calling, and accordingly presupposes a careful analysis of the special economical processes.  It is, indeed, easy to recognize that in certain industrial activities a series of psychical functions is in question which all lie side by side and which do not fuse into one united total process, however much they may influence one another.  But for many industrial tasks just this unity is the essential condition.  The testing of the mental elements would be in such cases as insufficient as if we were to test a machine with reference to its parts only and not with reference to its total united performance.  Even in this latter case this unified function does not represent the total personality:  it is always merely a segment of the whole mental life.  We may examine with psychological methods, for instance, the fitness of an employee for a technical vocation and may test the particular complex unified combination of attention, imagination and intelligence, will and memory, which is essential for that special kind of labor.  We may be able to reconstruct the conditions so completely that we would feel justified in predicting whether the individual can fulfill that technical task or not; and yet we may disregard entirely the question whether that man is honest or dishonest, whether he is pacific or quarrelsome; in short, whether his mental disposition makes him a desirable member of that industrial concern under other aspects.

We best recognize the significance of these various methods by selecting a few concrete cases as illustrations and analyzing them in detail.  But a word of warning may be given beforehand so as to avoid misunderstandings.  These examples do not stand here as reports of completed investigations, the results of which ought to be accepted as conclusive parts of the new psychotechnical science; they are not presented as if the results were to be recommended like a well-tested machine for practical purposes.  Such really completed investigations do not as yet exist in this field.  All that can be offered is modest pioneer work, and just these inquiries into the mental qualities and their relations to the industrial vocations have attracted my attention only very recently, and therefore certainly still demand long continuations of the experiments in every direction.  But we may hope for satisfactory results the earlier, the more cooeperators are entering the field, and the more such researches are started in other places and in other institutions.  I therefore offer these early reports at the first stage of my research merely as stimulations, so as to demonstrate the possibilities.

As an illustration of the method of examining the mental process as a whole, I propose to discuss the case of the motormen in the electric railways.  As an illustration of the other type, namely, of analyzing the activity and testing the elementary functions, I shall discuss the case of the employees in the telephone service.  I select these two functions, as both play a practically important role in the technique of modern economic life and as in both occupations very large numbers of individuals are engaged in the work.