STATUS OF FACTORS IN PSYCHOLOGY 11

mately composed, elements which he apparently would
identify with the ' neurone arcs ' of which the central
nervous system is built up.

It would seem, however, that what Thomson is treating
as the ultimate factors are something quite different from
what Spearman, Thurstone, Kelley, Alexander, and most
other psychologists have had in mind, namely, what they
would call the primary intellectual abilities—g, z>, c, F,
and the like. Spearman's * basic components ' are rather
like the organs of the body ; Thomson's are more like its
cells ; or (to adopt an analogy which both writers use)
Spearman's are like the £ parts ' of a motor-car—the wheels,
the lamps, the horn, the engine, and the tank containing the
petrol; Thomson's, more like the ultimate molecules of
which all the materials are composed. And there is this
further difference between them : Spearman looks upon
the mind as a heterogeneous structure built up out of a
few essential mechanisms or components; Thomson
insists that the mind is almost devoid of structure—a tissue
of homogeneous cells rather than an organized whole of
specialized parts,1

The Reasons for Factor-analysis.—What may be the
ultimate structure of the mind, and whether its parts are
numerous or few, and its elements similar or differentiated,
are questions, so at least it seems to me, which must be
eventually decided by other lines of research—physiological,
biological, introspective, and experimental.2 Our present
crude distinctions between intellectual abilities may give

1 The difference is largely one of emphasis. Thus, although in the passage
quoted and again on p. 280 he speaks of the mind as ' comparatively structure-
less,5 elsewhere (pp. 51 and 283) he describes the mind as divided into
* regions' or * subpools? and even admits that far t of this * structure ' may be
' innate/ though most of it is due to environment and education. Thus
qualified, his two statements are not incompatible, and are far less in conflict
with Spearman's than a first reading might suggest.

2 How the results of these alternative lines of inquiry are related to those
of factpr-analysis I have tried briefly to indicate elsewhere (e.g. [128],
pp. 191-5); it should be added, however, that not every exponent of mental
factors would admit the relevance of physiological or other evidence :
Stephenson, for example, has recently argued that my * endeavour to bring
physiology into the picture only confuses the issue.'