e to argue that all inference is from
particulars to particulars. Inference through a general proposition is not
necessary, yet useful as a collateral security, inasmuch as the syllogistic
forms enable us more easily to discover errors committed. The ground of
induction, the uniformity of nature in reference both to the coexistence
and the succession of phenomena, since it wholly depends on induction,
is not unconditionally certain; but it may be accepted as very highly
probable, until some instance of lawless action (in itself conceivable)
shall have been actually proved. Like the law of causation, the principles
of logic are also not _a priori_, but only the highest generalizations from
all previous experience.

Mill's most brilliant achievement is his theory of experimental inquiry,
for which he advances four methods: (1) The Method of Agreement: "If two
or more instances of the phenomenon under investigation have only one
circumstance in common, the circumstance in which alone all the instances
agree is the cause (or effect) of the given phenomenon." (2) The Method of
Difference: "If an instance in which the phenomenon under investigation
occurs, and an instance in which it does not occur, have every circumstance
in common save one, that one occurring only in the former; the circumstance
in which alone the two instances differ, is the effect, or the cause, or an
indispensable part of the cause, of the phenomenon," These two methods (the
method of observation, and the method of artificial experiment) may also be
employed in combination, and the Canon of the Joint Method of Agreement and
Difference runs: "If two or more instances in which the phenomenon occurs
have only one circumstance in common, while two or more instances in
which it does not occur have nothing in common save the absence of that
circumstance, the circumstance in which alone the two sets of instances
differ is the effect, or the cause, or an indispensable part of the
cause, of the phenomenon." (3) The Method of Residues: "Subduct from any
phenomenon such part as is known by previous inductions to be the effect of
certain antecedents, and the residue of the phenomenon is the effect of the
remaining antecedents." (4) The Method of Concomitant Variations: "Whatever
phenomenon varies in any manner whenever another phenomenon varies in some
particular manner, is either a cause or an effect of that phenomenon, or is
connected with it through some fact of ca