Q. Is “this is mine and Kelly’s cat” correct? Would you please
explain the rules behind this sentence. Thank you. A. Sorry—not
even close. Think about it: would we say “This is mine cat” (if
we are not Shakespeare)? Rather, we say “This is my cat,”
because the word that precedes a noun (“cat”) as a modifier must
be an adjective, like “my.” (The pronoun “mine,” however, can
serve as an adjective when it’s placed after a noun: the cat is
mine.) And since it’s polite and grammatical to put yourself
last in a list of people (a custom that dies a little more every
time someone says “Me and Jughead bought us a pit bull”), the
correct phrasing would be “This is Kelly’s and my cat,” or, less
awkwardly, “This cat is Kelly’s and mine.”