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 case,