that
feeling is not itself a feeling. But can I detect any relation between
these experiences of mine except that of succession? We commonly speak
of fire as the cause of the melting of the wax, but what do we really
know about the matter? Surely on reflection we must admit that we know
nothing but this--that, so far as our experience goes, the application of
fire is always followed by the melting of the wax. Where this is the
case we do, from the point of view of {33} ordinary life, speak of the
one phenomenon as the cause of the other. Where we don't discover such
an invariable succession, we don't think of the one event as the cause of
the other.

I shall be told, perhaps, that on this view of the nature of Causality we
ought to speak of night as the cause of day. So perhaps we should, if
the result to which we are led by a more limited experience were not
corrected by the results of a larger experience. To say nothing of the
valuable correction afforded by the polar winter and the polar summer, we
have learned by a more comprehensive experience to replace the law that
day follows night by the wider generalisation that the visibility of
objects is invariably coincident upon the presence of some luminous body
and not upon a previous state of darkness. But between cases of what we
call mere succession and what is commonly called causal sequence the
difference lies merely in the observed fact that in some cases the
sequence varies, while in others no exception has ever been discovered.
No matter how frequently we observe that a sensation of red follows the
impact upon the aural nerve of a shock derived from a wave of ether of
such and such a length, we see no reason why it should do so. We may, no
doubt, make a still wider generalization, and say that every event in
Nature is invariably preceded by some definite complex of conditions,
{34} and so arrive at a general law of the Uniformity of Nature. And
such a law is undoubtedly the express or implied basis of all inference
in the Physical Sciences. When we have once accepted that law (as the
whole mass of our experience in the purely physical region inclines us to
do), then a single instance of A B C being followed by D (when we are
quite sure that we have included all the antecedents which we do not know
from other experience to be irrelevant) will warrant our concluding that
we have discovered a law of nature. On the next occasion of A B C's
occurrence we