d
Russell, Baldwin, Urban, Montague, and others, and a new interest in
foreign works, German, French and Italian, which had either become
classical or were attracting public attention, had developed. The scope
of the Library thus became extended into something more international,
and it is entering on the fifth decade of its existence in the hope that
it may contribute to that mutual understanding between countries which
is so pressing a need of the present time."

The need which Professor Muirhead stressed is no less pressing to-day,
and few will deny that philosophy has much to do with enabling us to
meet it, although no one, least of all Muirhead himself, would regard
that as the sole, or even the main, object of philosophy. As Professor
Muirhead continues to lend the distinction of his name to the Library
of Philosophy it seemed not inappropriate to allow him to recall us to
these aims in his own words. The emphasis on the history of thought also
seemed to me very timely; and the number of important works promised
for the Library in the very near future augur well for the continued
fulfilment, in this and other ways, of the expectations of the original
editor.

H. D. Lewis

PREFACE

This book has grown out of an attempt to harmonize two different
tendencies, one in psychology, the other in physics, with both of which
I find myself in sympathy, although at first sight they might seem
inconsistent. On the one hand, many psychologists, especially those
of the behaviourist school, tend to adopt what is essentially a
materialistic position, as a matter of method if not of metaphysics.
They make psychology increasingly dependent on physiology and external
observation, and tend to think of matter as something much more solid
and indubitable than mind. Meanwhile the physicists, especially Einstein
and other exponents of the theory of relativity, have been making
"matter" less and less material. Their world consists of "events," from
which "matter" is derived by a logical construction. Whoever reads, for
example, Professor Eddington's "Space, Time and Gravitation" (Cambridge
University Press, 1920), will see that an old-fashioned materialism can
receive no support from modern physics. I think that what has permanent
value in the outlook of the behaviourists is the feeling that physics is
the most fundamental science at present in existence. But this position
cannot be called materialistic, if, as seems to be the c