reveals idealism, as it seems to me, resting insecurely
on a fallacy or two. And it may or may not be a mere
coincidence that one observes on several sides of the
philosophic world a tendency to dispute that claim
which idealism, of one form or another, has laid to being
the beginning at least of a final solution of the world-
problem. With the objections which by and large have
been raised against idealism we have here no immediate
concern, for it is the purpose of this book first to survey
briefly the findings of modern logic, and then to examine,
with as little bias as may be, their bearing on episte-
mology. Yet it is fair to say at the outset that if anyone
has foreseen the outcome of such an inquiry, that person
was Avenarius. ¹ For whatever may be the other merits
or the defects of that author's Empirio-Critical theory,
and I believe that the defects are several, he was the
first in modern times to 'exclude the introjection.'
And this exclusion we shall see is one of the lessons of
modern logic.

In order to understand the consequences for philos-
ophy of modern investigations in logic, we must take a
brief and tentative survey of what symbolic logic is and

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