244 Public Lectures
mediate contact. Our marvelously intricate complex of atoms
is equipped for perceiving, but is as yet totally incapable of
perception.
Our survey, beginning in the middle of the field of inani-
mate nature, has at this point brought us to its edge. We
discover that, as -physicists, we cannot step over the border-
line without sinking into a veritable quagmire of a queer sort
of immaterial substance. Indeed, even in probing into the
constitution of the human organism, we could not help feel-
ing that our purely physical analysis had banished something
quite essential from its natural habitat. Permeating what we
call a living organism is a subtle something which, under
physical analysis, slips away and escapes detection, leaving
behind a machine-like structure, capable of operating but
actually inoperative.
This, for Locke, is mind or “immaterial substance.” He
calls it substance, though it is nothing material, partly be-
cause it was the custom in his day to call anything real a sub-
stance or a property of substance, and partly because mind is,
in Locke’s conception, something that is really localized and
spread out in the same space through which matter moves.
Hence it is legitimately called substance, a “stuff” capable of
having distinctive properties of its own which distinguish it
from the stuff of matter. Just what these properties are we
shall see as the discussion proceeds, but let us first attempt to
understand clearly the relation between a mind and the body
it animates. This will keep us to the proposed line of investi-
gation.
Locke, showing his fine commonsense, says quite definitely
that the mind is where the body is. Whether this is true or
not, such a conception at least makes it possible to have fairly
“clear and distinct” ideas about the body-mind relation. To
some of us, it may seem unnecessary to argue the point, for