Use of logical
propositions¤ You may
have one so complicated that you cannot, by looking at it, see that it
is a tautology; but you have shewn that it can be derived by certain
operations from
|| certain other
propositions
which according to our rule for
constructing tautologies; & hence you are enabled to
see that one thing follows from another, when you would not have been
able to see it otherwise. E.g. if our
tautology is of
the form p ⊃ q, you
can see that q follows from p; & so on.