Some nouns form irregular plurals. Those ending in f change that letter to v and then add es; as, half, halves; leaf, leaves; wolf, wolves. Those ending in y change that to i and add the es; as, cherry, cherries; berry, berries; except when the y is preceded by a vowel, in which case it only adds the s; as, day, days; money, moneys (not ies); attorney, attorneys. All this is to make the sound more easy and harmonious. F and v were formerly used indiscriminately, in singulars as well as plurals, and, in fact, in the composition of all words where they occurred. The same may be said of i and y.
"The Fader (Father) Almychty of the heven abuf (above)
In the mene tyme, unto Juno his luf (love)
Thus spak; and sayd."
Douglas, booke 12, pag. 441.
"They lyued in ioye and in felycite
For eche of hem had other lefe and dere."
Chaucer, Monks Tale, fol. 81, p. 1.
"When straite twane beefes he tooke
And an the aultar layde."
The reason why y is changed into i in the formation of plurals, and in certain other cases, is, I apprehend, accounted for from the fact that words which now end in y formerly ended in ie, as may be seen in all old books. The regular plural was then formed by adding s.
"And upon those members of the bodie, which wee thinke most unhonest, put wee more honestie on." "It rejoyceth not in iniquitie—diversitie of gifts—all thinges edifie not." See old bible, 1 Cor., chap. 13 and 14.
Other words form their plurals still more differently, for which no other rule than habit can be given; as, man, men; foot, feet; tooth, teeth; die, dice; mouse, mice; penny, pence, and sometimes pennies, when applied to distinct pieces of money, and not to value.
Many foreign nouns retain the plural form as used by the nations from whom we have borrowed them; as, cherub, cherubim; seraph, seraphim; radius, radii; memorandum, memoranda; datum, data, &c. We should be pleased to have such words carried home, or, if they are ours by virtue of possession, let them be adopted into our family, and put on the garments of naturalized citizens, and no longer appear as lonely strangers among us. There is great aukwardness in adding the english to the hebrew plural of cherub, as the translators of the common version of the bible have done. They use cherub in the singular and cherubims in the plural. The s should be omitted and the Hebrew plural retained, or the preferable course adopted, and the final s be added, making cherubs, seraphs, &c. The same might be said of all foreign nouns. It would add much to the regularity, dignity, and beauty, of our vernacular tongue.