STATUS OF FACTORS IN PSYCHOLOGY 13

which they obey.? Thomson's starting-point., as he him-
self has .related, was an endeavour to improve the methods
of selecting pupils for different types of school and career
by scholastic examinations or by mental tests. I myself
would rather place the initial emphasis on a third and
somewhat lowlier purpose. It is one which, I am sure,
both parties would accept as equally obvious, yet at the
same time one which, just because it is so easily taken for
granted and perhaps because it is less ambitious, has been
continually passed by. In my view the primary object of
factorial methods is neither causal interpretation, nor
statistical prediction, but exact and systematic description.
And I suspect that most of the confusion has arisen because
factors, like the correlation coefficients on which they are
based, have been invoked to fulfil these three very different
purposes, and so have made their appearance at three very
different levels of thought—like the famous legal firm of
Arldes, Arkles & Arkles, which, " more to its own satisfaction
than that of its clients, canvassed three different lines of
business in three small offices on three different floors.5'