-fe>-ves

GENERAL RULE: The plural of most words ending in -f or -fe (scarf, life, knives…) ends in -ves:

scarf--scarves

half--halves

leaf--leaves

thief--thieves

loaf--loaves

wolf--wolves

self--selves

shelf--shelves

knife--knives

life--lives

wife--wives

A few words, however, can be spelt with both -fs and -ves:

wharf--wharfs/wharves

calf--calfs/calves

dwarf--dwarfs/dwarves

Finally, there are a few exceptions whose plural is only spelt -fs:

roof--roofs

proof--proofs

chief--chiefs

belief--beliefs

sheriff--sheriffs

giraffe--giraffes