Third person singular of 'behalve,' an archaic verb meaning it is a proper duty or necessity for someone; it behooves.
Archaic variant or cognate of 'behoove' (from Old English behōfian, be- + hōfian 'to need'). Related to the modern 'behoove' which still appears in formal English.
Behoove is still alive in legal and formal writing ('it behooves you'), but behalves is a dead variant—language naturally selects winners, and behoove won out probably just because it sounded better to speakers' ears over centuries.
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