AN, A.
A has an indefinite signification, and means one, with some reference to more; as This is a good book; that is, one among the books that are good; He was killed by a sword; that is, some sword; This is a better book for a man than a boy; that is, for one of those that are men than one of those that are boys; An army might enter without resistance; that is, any army.
In the senses in which we use a or an in the singular, we speak in the plural without an article; as these are good books.
I have made an the original article, because it is only the Saxon an, or æn, one, applied to a new use, as the German ein, and the French un; the n being cut off before a consonant in the speed of utterance.
Grammarians of the last age direct, that an should be used before h; whence it appears that the English anciently asperated less. An is still used before the silent h; as an herb, an honest man; but otherwise a; as
A horse, a horse, my kingdom for a horse. Shakespeare.
An or a can only be joined with a singular: the correspondent plural is the noun without an article, as, I want a pen, I want pens; or with the pronominal adjective some, as, I want some pens.