is indestructible_. Without this further ground there can be no
inference. The fact is that conditional forms often cover assertions
that are not true complex propositions but a sort of euthymemes (chap.
xi. § 2), arguments abbreviated and rhetorically disguised. Thus: _If
patience is a virtue there are painful virtues_--an example from Dr.
Keynes. Expanding this we have--

Patience is painful;
Patience is a virtue:
∴ Some virtue is painful.

And then we see the equivocation of the inference; for though patience
be painful _to learn_, it is not painful _as a virtue_ to the patient
man.

The hypothetical, '_If Plato was not mistaken poets are dangerous
citizens_,' may be considered as an argument against the laureateship,
and may be expanded (informally) thus: 'All Plato's opinions deserve
respect; one of them was that poets are bad citizens; therefore it
behoves us to be chary of encouraging poetry.' Or take this
disjunctive, '_Either Bacon wrote the works ascribed to Shakespeare, or
there were two men of the highest genius in the same age and country_.'
This means that it is not likely there should be two such men, that we
are sure of Bacon, and therefore ought to give him all the glory. Now,
if it is the part of Logic 'to make explicit in language all that is
implicit in thought,' or to put arguments into the form in which they
can best be examined, such propositions as the above ought to be
analysed in the way suggested, and confirmed or refuted according to
their real intention.