What is Meant by Function.--Several times in the text we
have had occasion to speak of functions. Now that we have ex-
amined most of the phases of an individual's acquisitions both of
the explicit and implicit kinds it seems well to get a more exact
formulation of what is meant by the term. After an act has
been acquired and used for a definite time and is then repeatedly
put away and again used, the learning and re-learning phases
and periods of no practice become of little consequence. We
assume that every normal individual can perform the acts re-
quired by a social environment and we do not care particularly
whether it took him a long time to learn them or a short time.
We are interested, in the discussion which follows, in the question
as to the rapidity and accuracy with which those habits work and
the factors which influence them. It is convenient to call each
organized habit system of an individual which is always ready
to act under appropriate stimulation, an acquired function, in
contrast to emotional and instinctive functions. (The total assets
of an individual are the sum of his hereditary and acquired
functions, his retentiveness and his plasticity. Examples of
such acquired functions are, of course, talking, walking, swim-
ming, addition, subtraction, writing and all similar ones discussed
in the preceding two chapters. As we use the term, it has no
fixed implication and is not a mathematical or even a rigidly
scientific one. A function is really, then, a phase of activity that
one happens to be studying and measuring; the acquired func-
tions are equivalent really to habits except for the fact that when
we use the term function we generally (but not even here always)
leave the genetic aspect out of consideration. New habits, if
continued, end always by giving us new functions. In studying
children (or adults if learning) the term habit is emphasized;
in studying adults the term function is most frequently met with,

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