denied; (2) a Predicate (as _soluble in water_) which is asserted or
denied of the Subject, and (3) the Copula (_is_ or _are_, or _is not_ or
_are not_), the sign of relation between the Subject and Predicate. The
Subject and Predicate are called the Terms of the proposition: and the
Copula may be called the sign of predication, using the verb 'to
predicate' indefinitely for either 'to affirm' or 'to deny.' Thus _S is
P_ means that the term _P_ is given as related in some way to the term
_S_. We may, therefore, further define a Proposition as 'a sentence in
which one term is predicated of another.'

In such a proposition as _Salt dissolves_, the copula (_is_) is
contained in the predicate, and, besides the subject, only one element
is exhibited: it is therefore said to be _secundi adjacentis_. When all
three parts are exhibited, as in _Salt is soluble_, the proposition is
said to be _tertii adjacentis_.

For the ordinary purposes of Logic, in predicating attributes of a thing
or class of things, the copula _is_, or _is not_, sufficiently
represents the relation of subject and predicate; but when it is
desirable to realise fully the nature of the relation involved, it may
be better to use a more explicit form. Instead of saying
_Salt--is--soluble_, we may say _Solubility--coinheres with--the nature
of salt_, or _The putting of salt in water--is a cause of--its
dissolving_: thus expanding the copula into a full expression of the
relation we have in view, whether coinherence or causation.

§ 3. The sentences of ordinary discourse are, indeed, for the most
part, longer and more complicated than the logical form of propositions;
it is in order to prove them, or to use them in the proof of other
propositions, that they are in Logic reduced as nearly as possible to