LAWS OF NATURE.
The uniformity of the course of nature is a complex fact made up of all
the separate uniformities in respect to single phenomena. Each of these
separate uniformities, if it be not a mere case of and result from
others, is a law of nature; for, though _law_ is used for any general
proposition expressing a uniformity, _law of nature_ is restricted to
cases where it has been thought that a separate act of creative will is
necessary to account for the uniformity. Laws of nature, in the
aggregate, are the fewest general propositions from which all the
uniformities in the universe might be deducted. Science is ever tending
to resolve one law into a higher. Thus, Kepler's three propositions,
since having been resolved by Newton into, and shown to be cases of the
three laws of motion, may be indeed called laws, but not laws of nature.
Since every correct inductive generalisation is either a law of nature,
or a result from one, the problem of inductive logic is to unravel the
web of nature, tracing each thread separately, with the view, 1, of
ascertaining what are the _several_ laws of nature, and, 2, of following
them into their results. But it is impossible to frame a scientific
method of induction, or test of inductions, unless, unlike Descartes, we
start with the hypothesis that some trustworthy inductions have been
already ascertained by man's involuntary observation. These spontaneous
generalisations must be revised; and the same principle which common
sense has employed to revise them, correcting the narrower by the wider
(for, in the end, experience must be its own test), serves also, only
made more precise, as the real type of scientific induction. As
preliminary to the employment of this test, nature must be surveyed,
that we may discover which are respectively the invariable and the
variable inductions at which man has already arrived unscientifically.
Then, by connecting these different ascertained inductions with one
another through ratiocination, they become mutually confirmative, the
strongest being made still stronger when bound up with the weaker, and
the weakest at least as strong as the weakest of those from which they
are deduced (as in the case of the Torricellian experiment) while those
leading deductively to incompatible consequences become each other's
test, showing that one must be given up (e.g. the old farmers' bad
induction that seed never throve if not sown during the increase of the
moon). It is because a survey of the uniformities ascertained to exist
in nature makes it clear that there are certain and universal
uniformities serving as premisses whence crowds of lower inductions may
be deduced, and so be raised to the same degree of certainty, that a
logic of induction is possible.