The plural thieves is an exception, since the other nouns belief, brief, chief, and relief all form normal plurals with an S. But note that the verb forms believes and relievesare like the verb "thieves" (robs).
The adoption of words into English from other languages creates various pronunciations, and the spelling usually reflects that. But there seems to be no reason why the form "thiefs" is not used.
(The word "thief" comes from the Germanic theof so we cannot blame the French.)
It is actually somewhat arbitrary, but some nouns already has an -ieves form that has a different meaning.
Examples of plural nouns:
brief - briefs (which is also the verb)
belief - beliefs (verb is believes)
thief - thieves (which is also the verb)
Note that relief and grief do not normally form plurals, but have -ieves verb forms.
There is no logical principle at work here. There are many inconsistencies in English spelling. English spelling results from many different influences, which are not always harmonized.
The words ending in -ief can form normal plurals. In this case, it is chiefs.An example of the other form is thief, which becomes thieves.
The noun daffodil has a normal S plural, daffodils.
The plural of thief is thieves.The more rarely used verb (robs) also has the third-person singular form thieves.
The plural of kerchief is kerchiefs - not kerchieves, so the plural of handkerchief is handkerchiefs - not alternatives which is copping out. The same as the plural of thief is thieves and not thiefs. There must be some grammatical or maybe contextual rule about this, but I cannot see it. Does anybody know, or do we have to remember all of these archaic rules of spelling rather than applying a rule that can be applied to all nouns ending in ief? I thought of verbs that could also be gerunds, or nouns that were also verbs - such a thieving, but not handkerchieving, but that fails when we consider a belief and believing in its plural being beliefs. So there are no apparent rules: does anybody know of any universal law of spelling that meets my believes - sorry, beliefs? Chiefs can chief but thiefs cannot thief - so is that it? The verb form? If you can thieve then you are thieves and thieving, and if you can chief then your are chiefs and chiefing? But how about belief and beliefing? That doesn't work. There must be a rule there somewhere! I am confused - anybody any ideas? Pete article-services.com P.S.: I spell-checked this, and thiefs, chiefing and beliefing were all wrong - I know that, so where do we go from here? Later addition by Pete: I have thought on this, and: More than one thief thieves, and plural is thieves More than one chief doesn't chieve, so plural isn't chieves More than one belief is beliefs, so plural is beliefs (Obviously) More than one brief doen't brieve so plural is briefs ? There is an inkling of a pattern there - isn't their? Or maybe it's just that there are so few words ending in 'ief' that nobody has a clue what their plural is!
The plural way to spell studio is studios.
The words ending in -ief can form normal plurals. In this case, it is chiefs.An example of the other form is thief, which becomes thieves.
It is a normal S plural, worms.
The plural is a normal one, horoscopes.
The plural is a normal S plural, associates.
The plural of "race" is "races."
The word forms the normal plural nods.
The noun rescue forms a normal plural : rescues.
The noun nominee has a normal S plural, nominees.
The word apostrophe has the normal S plural apostrophes.
The noun daffodil has a normal S plural, daffodils.
The word trampoline forms a normal S plural, trampolines.
The plural of loaf is loaves. Some, but not all words ending in F change it to a V and add -es to form the plural (thief-thieves, hoof-hooves).