Originally Posted by Kate Colombo:
The most often seen error seems to be the double possessive. Someone will write. Is she a friend of your sister's?
Your sister's what? Chihuahua?
It's simply: She's a friend of my sister.
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And folks pay good money to have those little plaques painted up to put in their yards or on their porches, proclaiming that "The Brown's" or "The Smith's" occupy the premises.