266. An Exclusive Proposition is so called because in it all but a
given subject is excluded from participation in a given predicate,
e.g. 'The good alone are happy,' 'None but the brave deserve the
fair,' 'No one except yourself would have done this.'

267. By the above forms of expression the predicate is declared to
apply to a given subject and to that subject only. Hence an exclusive
proposition is really equivalent to two propositions, one affirmative
and one negative. The first of the above propositions, for instance,
means that some of the good are happy, and that no one else is so. It
does not necessarily mean that all the good are happy, but asserts
that among the good will be found all the happy. It is therefore
equivalent to saying that all the happy are good, only that it puts
prominently forward in addition what is otherwise a latent consequence
of that assertion, namely, that some at least of the good are happy.

268. Logically expressed the exclusive proposition when universal
assumes the form of an E proposition, with a negative term for its
subject

No not-A is B.

269. Under the head of exclusive comes the strictly particular
proposition, 'Some A is B,' which implies at the same time that 'Some
A is not B.' Here 'some' is understood to mean 'some only,' which is
the meaning that it usually bears in common language. When, for
instance, we say 'Some of the gates into the park are closed at
nightfall,' we are understood to mean 'Some are left open.'