loz THE FACTORS OF THE MIND

about the traits, and (as we shall see in a moment) analogous
propositions can also be asserted about the persons :

(1) All the traits possess a particular characteristic, g, and thus
form a general, all-inclusive class ;

(2) Some of the traits possess a particular characteristic, fa
(which the rest do not possess), and thus form a narrower sub-class;
and again others possess the characteristic p2 (which the rest do
not possess) and thus form a second sub-class ; and so on ;

(3) This particular trait possesses one particular set of character-
istics, u^ which none of the others possess and which thus, as it
were, forms a sub-class of one ; and similarly for each of the other
traits.

Further, if we repeat our tests, we may be able to add that
this particular trait possesses (a) one particular set of characteristics,
SD always, i.e. every time we measure it (the series of repeated
measurements thus forming, as it were, a sub-subclass), and (b)
other sets of characteristics, ev e%, ... occasionally, i.e. one set on
this occasion, another on that.1

These four possibilities indicate four main kinds of factors.
They may be conveniently designated (as I have elsewhere *
suggested) by the labels traditionally used by logicians in
classifying propositions according to their ^quantity,' They
fall into two main groups, each of which may be redivided
into two :

A. Common factors, i.e. those influencing several tests or traits.
These are of two kinds, viz. :

(i) Universal or General factors, common to all the traits.
Later we shall see that the general factors in their turn may take
two different forms :

(a) Positive or One-signed factors, i.e. factors which can vary
in one direction only, viz. above zero, never below, and whose
saturation coefficients can therefore take positive values only.
Usually only one such positive universal factor is distinguish*:
able, which is then termed (the general factor 9;

1 The student of logic may remember somewhat similar distinctions
introduced by the schoolmen in their classification of properties: viz. id
quod pertinet (i) omni, (ii) non omni, (iii) semper, (iv) non semper,

8 Marks of Examiners, p. 259, and earlier writings.