Kenneth G. Wilson (1923). The Columbia Guide to Standard American English. 1993.
NOUNS ENDING IN -F, -FE: SPELLING AND PRONUNCIATION OF PLURALS AND FUNCTIONAL SHIFTS TO VERBS
Some of these words add -s to make the plural; far more replace the -f or -fe with -ves for the plural. All reflexive pronouns add -ves: yourself becomes yourselves; myself becomes ourselves; himself, herself, and itself become themselves. Still other words do both, sometimes with a semantic distinction between the plurals. The spellings reflect the pronunciations of these consonants, an f sound for the voiceless one in, for example, wife (WEIF), a v sound for the voiced one in wives (WEIVZ).
Calf (the animal) has two plurals, calves and calfs. The part of the leg has one plural, calves. The verb meaning to give birth to a calf is calve, and the participial adjective meaning provided with calves (on the legs) is calved.
Handkerchief has two plural spellings, handkerchiefs and the less-common handkerchieves. The first spelling is sometimes pronounced with the v sound of the second.
Hoof has two plural spellings, hoofs and hooves, and the pronunciations of singular, plurals, and genitives reflect the two vowels: HOOF and HUF. The slang verbs past tense is hoofed, as is the adjective.
Leaf has a plural, leaves, with a participial adjective, leaved. But the past tense of leaf (turning the pages of a book) is leafed; the past tense of leaf (growing leaves) may be either leafed or leaved.
Life has a plural, lives, with the same vowel. The participial adjective (as in long-lived) has a v in place of the f, but the second element of the combination may have either a long vowel (rhyming with drive) or a short vowel (rhyming with give). The plural of still life is still lifes.
Scarfs plural is scarves for the neckwear but scarfs for the carpenters joints. The past participle of the verb meaning provided with a scarf to wear and the past tense of the carpenters verb are both scarfed.
Staffs plural is staffs, except for the music staves and barrel staves, both pronounced to rhyme with braves. (The music staff also can have staffs as a plural.) The verb staff has a past tense and past participle staffed.