notの短縮形は前の語と結びついて「-n't」となるものが多いです。
[いろいろな語と結びついたnotの短縮形]
is not → isn't
are not → aren't
do not → don't
does not → doesn't
can not → can't
He is not a doctor. → He isn't a doctor.(彼は医者ではありません)
They do not play baseball. → They don't play baseball. (彼らは野球をしません)