Some are entirely anomalous, as, die, dice; penny, pence; goose, geese; sow, swine; and brother makes brethren[10], when denoting persons of the same society or profession. Die, a stamp for coining, makes dies in the plural.
Index makes in the plural indexes, when it expresses a table of contents, and indices, when it denotes the exponent of an algebraic quantity.
Some are used alike in both numbers, as, hose[11], deer, sheep, these being either singular or plural.
Nouns expressive of whatever nature or art has made double or plural have no singular, as, bowels, lungs, scissors, ashes, bellows.
Nouns ending in y impure form their plural by changing y into ies, as quality, qualities.
Nouns purely Latin, Greek, Hebrew, French, &c., retain their original plurals.
| Sing. | Pl. | |
| Lat. | Arcanum | Arcana |
| Fr. | Beau | Beaux |
| Lat. | Erratum | Errata |
| Fr. | Monsieur | Messieurs, Messrs. |
| Heb. | Cherub | Cherubim |
| Heb. | Seraph | Seraphim |
| Lat. | Magus | Magi |
| Gr. | Phenomenon | Phenomena |
| Lat. | Stratum | Strata |
| Gr. | Automaton | Automata |
| Lat. | Vortex | Vortices |
| Lat. | Radius | Radii |
| Lat. | Genus | Genera |
| Gr. | Crisis | Crises |
| Gr. | Emphasis | Emphases |
| Gr. | Hypothesis | Hypotheses |
| Lat. | Genius | Genii, |
when denoting aërial spirits; but when signifying men of genius, or employed to express the plural of that combination of mental qualities which constitutes genius, it follows the general rule.
A proper name has a plural number when it becomes the name of more individuals than one, as, the two Scipios; the twelve Cæsars. It is to be observed, however, that it ceases then to be, strictly speaking, a proper name.