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