METAPHYSICAL STATUS OF FACTORS 227

conclusion seems clear. Rigorously speaking, factors cannot
be regarded as substances, or as parts of a substance, or even
as causal attributes inhering in a substance. They are not
separatec organs ' or isolatedc properties ' of the mind ; they
are not; primary abilities/ ' unitary traits,5 ' mental powers
or energies.' They are principles of classification described
by selective operators. The operand on which these operators
operate is not ' the mind' but the sum total of the relations
between minds and their environment. The relational
structure of this operand the factorist must presume to be
knowable, but its causal or substantial nature he must treat
as unknown or at any rate irrelevant.1

Three Levels of Interpretation.—Without launching into
the more elusive problems of epistemology, we may, I think,
clarify and harmonize the conflicting views put forward on
the reality and causal efficacy of mental factors, if we recall
the three distinct aims of reasoned analysis—prediction,
explanation, and description. These broadly correspond
to the three ways in which man has progressively approached
the study of the world around him—the practical, and then
the philosophical, and finally the scientific. In sciences
that do not deal with man himself the non-scientific
issues are less prone to obtrude. The botanist, as he
classifies his field specimens, does not worry whether herb
robert would develop better if transferred to garden soil,
or speculate whether the beauty of each fading rose is
transcendentally immortal. But the psychologist, par-
ticularly if he is also a factorist, is continually running into
problems that are not scientific at all, but sometimes prac-
tical and sometimes metaphysical. He cannot avoid them.
For him, therefore, it is of supreme importance to keep the
different planes of thinking separate.

The practical thinker is interested chiefly in forecasting
the effects of alternative courses of action : the medical
psychologist at the clinic, for example, wants to know what
to do with his patient in the near future, and what will be the
ultimate outcome ; like most practical workers, he feels that,

1 I add irrelevant, because It is conceivable that the intrinsic nature and
causative operations of the mind might be revealed by introspection or
tentatively deduced by metaphysical speculation.