A System of Logic: Ratiocinative and Inductive, 7th Edition, Vol. II
John Stuart Mill · en
they are who act in that particular way; but we have seldom the means of
knowing whether any individual person has been under the influence of
those causes, or is a person of that particular sort. We could replace
the approximate generalizations by propositions universally true; but
these would hardly ever be capable of being applied to practice. We
should be sure of our majors, but we should not be able to get minors to
fit: we are forced, therefore, to draw our conclusions from coarser and
more fallible indications.
§ 4. Proceeding now to consider, what is to be regarded as sufficient
evidence of an approximate generalization; we can have no difficulty in
at once recognising that when admissible at all, it is admissible only
as an empirical law. Propositions of the form, Every A is B, are not
necessarily laws of causation, or ultimate uniformities of coexistence;
propositions like Most A are B _cannot_ be so. Propositions hitherto
found true in every observed instance, may yet be no necessary
consequence of laws of causation, or of ultimate uniformities, and
unless they are so, may, for aught we know, be false beyond the limits
of actual observation: still more evidently must this be the case with
propositions which are only true in a mere majority of the observed
instances.
There is some difference, however, in the degree of certainty of the
proposition, Most A are B, according as that approximate generalization
composes the whole of our knowledge of the subject, or not. Suppose,
first, that the former is the case. We know only that most A are B, not
why they are so, nor in what respect those which are, differ from those
which are not. How then did we learn that most A are B? Precisely in the
manner in which we should have learnt, had such happened to be the fact,
that all A are B. We collected a number of instances sufficient to
eliminate chance, and having done so, compared the number of instances
in the affirmative with the number in the negative. The result, like
other unresolved derivative laws, can be relied on solely within the
limits not only of place and time, but also of circumstance, under which
its truth has been actually observed; for as we are supposed to be
ignorant of the causes which make the proposition true, we cannot tell
in what manner any new circumstance might perhaps affect it. The
proposition, Most judges are inaccessible to bribes, would be found true
of Englishmen, Frenchmen, Germans, North Americans, and so forth; but if
on this evidence alone we extended the assertion to Orientals, we should
step beyond the limits, not only of place but of circumstance, within
which the fact had been observed, and should let in possibilities of the
absence of the determining causes, or the presence of counteracting
ones, which might be fatal to the approximate generalization.