DERIVATION OF CHIEF THEORIES 141

wide range, such as general intelligence, general emotion-
ality, and the like, and factors of a more restricted range,
such as the verbal factor, the manual factor, the factor
which contrasts introverts with extraverts, etc. The former,
as it were, state the genus, the latter the species or the type.
As we shall see later on, the initial inclusion of individual
or specific factors (as the psychologist uses the term specific1)
is little more than a prefatory acknowledgment on the part
of the theorist that, however much he proceeds to generalize,
his tests are after all particular tests and his persons par-
ticular persons, just as his initial inclusion of a set of error
factors is an admission that all measurements and assess-
ments, particularly those of psychological traits, are approxi-
mations only. Both are irrelevant to his main problem.
No psychologist, so far as I know, has ever calculated a
person's factor-measurement for any specific factor. If,
therefore, we hold that the specific factors, like the chance
factors, are devoid of all psychological interest on their
own account, and may be dismissed as unwelcome intruders
whose influence has to be reduced to negligible proportions
because it cannot be wholly dispelled, then we are left with
two noteworthy kinds of factors only—the general and the
group.

(d) 'The Two-factor Theory.—In the past, however, it has
been not the specific factors, but the group-factors, whose
importance—and even existence—has most commonly been
denied ; and it is the latter that have furnished the chief

1 In my own earlier writings (e.g. Child Study, he. cit. sup., p. 98 f.), I
used the term * specific } (and later * special') to designate factors or attributes
characteristic of a £ species'—i.e. what are now most commonly called
* group-factors * or * type-factors.' Owing, however, to the popular use of
' specific' as a synonym for £ peculiar,' the term has come to be applied
by psychologists to designate what might have been called, with less
ambiguity, a * peculiar,' c individual,' * unique,' or * singular' factor :
but these words, though occasionally employed by certain writers, have been
avoided by most, presumably because in colloquial speech they convey the
notion of something exceptional or bizarre. Accordingly, I shall here fall
in with the present custom, and restrict the word * specific * to the narrower
sense. Thurstone's definition is clear: " By a specific factor or ability is
meant any factor or ability which is called for by only one of the n tests"
([84], p. 54). Thomson, Holzinger, and most other writers now adopt the
same meaning; and any change of usage would only create confusion.