If the poet of the "Rape of the Lock" be not a wit, who deserves to be called so?—Thackeray.

He had a little brother in London with him at this time,—as great a beauty, as great a dandy, as great a villain.—Id.

A youth to fortune and to fame unknown.—Gray.

Changes material to class nouns.

191. An or a before a material noun indicates the change to a class noun, meaning one kind or a detached portion; as,—

They that dwell up in the steeple,...
Feel a glory in so rolling
On the human heart a stone.
—Poe.

When God at first made man,
Having a glass of blessings standing by.
—Herbert.

The roofs were turned into arches of massy stone, joined by a cement that grew harder by time.—Johnson.

Like the numeral adjective one.

192. In some cases an or a has the full force of the numeral adjective one. It is shown in the following:—