UNIFORMITIES OF COEXISTENCE NOT DEPENDENT ON CAUSATION.
Besides uniformities of succession, which always depend on causation,
there are uniformities of coexistence. These also, whenever the
coexisting phenomena are effects of causes, whether of one common cause
or of several different causes, depend on the laws of their cause or
causes; and, till resolved into these laws, are mere empirical laws. But
there are some uniformities of coexistence, viz. those between the
ultimate properties of _kinds_, which do not depend on causation, and
therefore seem entitled to be classed as a peculiar sort of laws of
nature. As, however, the presumption always is (except in the case of
those _kinds_ which are called _simple substances_ or elementary natural
agents), that a thing's properties really depend on causes though not
traced, and we _never_ can be certain that they do not; we cannot safely
claim (though it _may_ be an ultimate truth) higher certainty than that
of an empirical law for any generalisation about coexistence, that is to
say (since _kinds_ are known to us only by their properties, and,
consequently, all assertions about them are assertions about the
coexistence of something with those properties), about the properties of
_kinds_.
Besides, no rigorous inductive system can be applied to the uniformities
of coexistence, since there is no general axiom related to them, as is
the law of causation to those of succession, to serve as a basis for
such a system. Thus, Bacon's practical applications of his method
failed, from his supposing that we can have previous certainty that a
property must have an invariable coexistent (as it must have an
invariable antecedent), which he called its form. He ought to have seen
that his great logical instrument, elimination, is inapplicable to
coexistences, since things, which agree in having certain apparently
ultimate properties, often agree in nothing else; even the properties
which (e.g. Hotness) are effects of causes, generally being not
connected with the ultimate resemblances or diversities in the objects,
but depending on some outward circumstance.
Our only substitute for an universal law of coexistence is the ancients'
induction _per enumerationem simplicem ubi non reperitur instantia
contradictoria_, that is, the improbability that an exception, if any
existed, could have hitherto remained unobserved. But the certainty thus
arrived at can be only that of an empirical law, true within the limits
of the observations. For the coexistent property must be either a
property of the _kind_, or an accident, that is, something due to an
extrinsic cause, and not to the _kind_ (whose own indigenous properties
are always the same). And the ancients' class of induction can only
prove that _within given limits_, either (in the latter case) one
common, though unknown, cause has always been operating, or (in the
former case) that no new _kind_ of the object has _as yet_ or _by us_
been discovered.
The evidence is, of course (with respect both to the derivative and the
ultimate uniformities of coexistence), stronger in proportion as the law
is more general; for the greater the amount of experience from which it
is derived, the more probable is it that counteracting causes, or that
exceptions, if any, would have presented themselves. Consequently, it
needs more evidence to establish an exception to a very general, than to
a special, empirical law. And common usage agrees with this principle.
Still, even the greater generalisations, when not based on connection by
causation, are delusive, unless grounded on a separate examination of
_each_ of the included _infimae species_, though certainly there is a
probability (no more) that a sort of parallelism will be found in the
properties of different kinds; and that their degree of unlikeness in
one respect bears some proportion to their unlikeness in others.