calf elf *dwarf knife half *handkerchief *hoof leaf life loaf *scarf self sheaf shelf wife wolf
What do the words in the list above have in common? They all have irregular plural forms. The final <f> is replaced by <ves> and this ending is pronounced vz. The words marked with * have regular plurals for some speakers.
Notice that this applies only to the plural form. The possessive form with added <‘s> is perfectly regular. So for example wife – wife’s (waɪfs).
Not all nouns which end in <f> are irregular. Here are some which simply add <s> and this is of course pronounced s.
chief grief gulf oaf proof safe serf strife
By the way, calf and half have a silent <l>. Elf, self, shelf and wolf do not.
Finally, the word roofs can be pronounced either ruːfs or ruːvz, but it is not spelled <rooves>ǃ
Update: Alex Rotatori informs me that the spelling <rooves> is given by some dictionaries. I certainly wouldn’t recommend it though.