'horse.'_ They are partial or complete definitions.

But (c) there are also Real Propositions, whose predicates do not mean
the same as their subjects, and whose import consists in affirming or
denying one of five different kinds of matter of fact: (1) That the
subject exists, or does not; as if we say _The bison exists_, _The great
auk is extinct_. (2) Co-existence, as _Man is mortal_; that is, _the
being subject to death coinheres with the qualities on account of which
we call certain objects men_. (3) Succession, as _Night follows day_.
(4) Causation (a particular kind of Succession), as _Water rusts iron_.
(5) Resemblance, as _The colour of this geranium is like that of a
soldier's coat_, or _A = B_.

On comparing this list of real predications with the list of logical
relations given above (chap. i. § 5 (a)), it will be seen that the two
differ only in this, that I have there omitted simple Existence. Nothing
simply exists, unrelated either in Nature or in knowledge. Such a
proposition as _The bison exists_ may, no doubt, be used in Logic
(subject to interpretation) for the sake of custom or for the sake of
brevity; but it means that some specimens are still to be found in N.
America, or in Zoological gardens.

Controversy as to the Import of Propositions really turns upon a
difference of opinion as to the scope of Logic and the foundations of
knowledge. Mill was dissatisfied with the "congruity" of concepts as the
basis of a judgment. Clearly, mere congruity does not justify belief. In
the proposition _Water rusts iron_, the concepts _water_, _rust_ and
_iron_ may be congruous, but does any one assert their connection on
that ground? In the proposition _Murderers are haunted by the ghosts of
their victims_, the concepts _victim_, _murderer_, _ghost_ have a high