HO THE FACTORS OF THE MIND

ligence ; secondly, one or more special or ' group ' factors,
shared only by a limited number of intellectual processes ;
and thirdly, specific or individual factors^ peculiar to each
particular test itself " : x the theorem may be succinctly
expressed as an equation by writing —

where the symbols and summation have the same meaning
as before. In this early formulation I referred primarily to
intellectual traits, since in those days factor-analysis had
been almost entirely confined to the results of cognitive
tests : but at the same time I indicated that precisely the
same theorems could be applied to the factorization of
emotional, moral, or temperamental traits.2

(c) The Dual-factor Theory. — Here the important dis-
tinction to my mind lies between the general factors and
the special or group-factors. From a material as opposed
to a merely formal standpoint, the significant and fruitful
contrast is the contrast between factors of a comparatively

1 This formulation is taken from my Historical Introduction to Report on
Psychological Tests of Educable Capacity, Consultative Committee of the
Board of Education, 1924, p. 19, However, I first suggested expanding the
* two-factor theory ' into a * three-factor theory * in a paper read to the
Manchester Child Study Society in 1909 on * The Experimental Study of
Intelligence' (cf. [17], pp. 94 et j^.). The evidence then cited for the
addition of a third type of factor was the work at Oxford mentioned below,
confirmed by later work on ' higher mental processes ' by means of group
tests. On this basis I argued that we must " distinguish between (i) capa-
cities applicable in one direction only, (ii) capacities applicable in several
directions, and (iii) capacities applicable in all " ; and quoted Carlyle's
" favourite antithesis between * fundamental greatness ' (c the truly great
men could be all sorts of men ') and * varieties of aptitude ' (' Nature does not
make all great men, any more than all other men, in the self-same mould ')."
The main distinction, however, is as old as Aristotle : * Some persons,' he
declares, * are wise in all respects ' (<n><£ot 0X0)5), * others wise in parts *
(Kara /x,€/)os. Nic. Etb.9 VI, vii, 2). Binet, it may be remembered, similarly
contrasts * general intelligence * with f partial aptitudes/ and just before his
death was planning to supplement his scale of intelligence tests with measure-
ments of other abilities.

2 Cf. Annual Report Brit, Ass., * General and Specific Factors Underlying
the Primary Emotions/ 1915, pp. 694-6, and, for fuller arguments in favour
of this extension, see Character and Personality^ VII, pp. 238 et $eq,, ' The
Factorial Analysis of Emotional Traits.'