All truth and all error lie in Propositions.--J. S. Mill.
In accordance with that experience which directs to the profoundest
books for the simplest statements, we turn to Mill's Logic for the
philosophy of propositions. The answer to every question which it is
possible to frame is contained in a proposition or assertion. Whatever
can be an object of belief or even of disbelief, must, when put into
words, assume the form of a proposition * * What we call a truth is
simply a true proposition; and errors are false propositions. To know
the import of all possible propositions would be to know all questions
which can be raised, all matters which are susceptible of being either
believed or disbelieved. * * Since then the objects of all belief and
all inquiry express themselves in propositions, a sufficient scrutiny
of propositions and of their varieties will apprise us what questions
mankind have asked themselves, and what it the nature of the answers to
those questions they have actually thought they had grounds to believe.
'Now the first glance at a proposition shows that it is formed by
putting together two names. A proposition, according to the common
simple definition, which is sufficient for our purpose, is, _discourse
in which something is affirmed or denied of something_. Thus, in the
proposition, gold is yellow, the quality _yellow_ is affirmed of the
substance _gold_. In the proposition, Franklin was not born in England,
the fact expressed by the words _born in England_ is denied of the man
Franklin.
'Every proposition consists of three parts: the subject, the predicate,
and the copula. The predicate is the name denoting that which is
affirmed or denied. The subject is the name denoting the person or
thing which something is affirmed or denied of. The copula is the sign
denoting that there is an affirmation or denial; and thereby enabling
the hearer or reader to distinguish a proposition from any other kind of
discourse. Thus, in the proposition, the earth is round, the predicate
is the word _round_, which denotes the quality affirmed, or (as the
phrase is) predicated: _the earth_ words denoting the object which that
quality is affirmed of, compose the subject; the word it, which serves
as the connecting mark between the subject and predicate, to show that
one of them is affirmed of the other, is called the copula.'