22	THE  FACTORS OF THE MIND
dropped into the same error when dealing with conclusions
suggested by a tabulated pattern of correlations. Under
what special conditions, then, if at all, are we justified in
making such generalizations ?
Most psychologists who have used factor-analysis, at any
rate in this country, have regarded it as providing a means
of inferring, from'experiments on typical groups, funda-
mental laws of cognition holding good of all mental pro-
cesses wherever they are found. To derive laws from
limited facts, to argue from the behaviour of the sample to
the behaviour of the total population, is to argue from the
particular to the general; it is, in short, to reason by induc-
tion. And many of the criticisms laid at the door of the
factorist prove, when closely considered, to be criticisms,
not (as is generally supposed) of the mathematical method
of analysis adopted, but rather of the logic, or lack of logic,
which the factorial arguments display. What Fisher says
of the mathematicians' views about the analysis of variance
is equally true of psychologists' views about analysis by
factors: " many, if pressed, would say it is not possible to
argue rigorously from the particular to the general, that all
such arguments must involve some sort of guesswork, which
they might admit to be plausible guesswork, but the ration-
ale of which they would be unwilling to discuss/' * Yet,
as he himself adds, though we may frankly acknowledge
that all such inferences " must be attended with un-
certainty, this is not the same as to admit that such infer-
ences cannot be absolutely rigorous."
Accordingly, it seems worth while considering in some
detail why the inferences and the predictions of the
psychological factorist appear so lacking in rigour. I
propose, therefore, to examine the chief postulates or
principles which, implicitly or explicitly, have been relied
upon by factorial writers to increase the credibility of their
conclusions, and incidentally I shall endeavour to set down
what, to my view at any rate, are the commonest logical
defects of such work. As a rule, the supposed weakness of
^1 [*°9l P- 4' Thurstone, for example, declares: ** It is in the nature of
science that no scientific law can ever be proved to be right; it can only be
shown to be plausible " ([84], p. 45),