ogy.

If we have been right in our analysis of mind, the ultimate data of
psychology are only sensations and images and their relations. Beliefs,
desires, volitions, and so on, appeared to us to be complex phenomena
consisting of sensations and images variously interrelated. Thus (apart
from certain relations) the occurrences which seem most distinctively
mental, and furthest removed from physics, are, like physical objects,
constructed or inferred, not part of the original stock of data in the
perfected science. From both ends, therefore, the difference between
physical and psychological data is diminished. Is there ultimately
no difference, or do images remain as irreducibly and exclusively
psychological? In view of the causal definition of the difference
between images and sensations, this brings us to a new question, namely:
Are the causal laws of psychology different from those of any other
science, or are they really physiological?

Certain ambiguities must be removed before this question can be
adequately discussed.

First, there is the distinction between rough approximate laws and
such as appear to be precise and general. I shall return to the former
presently; it is the latter that I wish to discuss now.

Matter, as defined at the end of Lecture V, is a logical fiction,
invented because it gives a convenient way of stating causal laws.
Except in cases of perfect regularity in appearances (of which we can
have no experience), the actual appearances of a piece of matter are not
members of that ideal system of regular appearances which is defined
as being the matter in question. But the matter is, after all, inferred
from its appearances, which are used to VERIFY physical laws. Thus, in
so far as physics is an empirical and verifiable science, it must assume
or prove that the inference from appearances to matter is, in general,
legitimate, and it must be able to tell us, more or less, what
appearances to expect. It is through this question of verifiability and
empirical applicability to experience that we are led to a theory of
matter such as I advocate. From the consideration of this question it
results that physics, in so far as it is an empirical science, not a
logical phantasy, is concerned with particulars of just the same sort
as those which psychology considers under the name of sensations. The
causal laws of physics, so interpreted, differ from those of psychology
only by the fact that they connect a