An apostrophe can show possession, as in the dog's bowl, or mark missing letters in a contraction.

The longer version

One mark does two different jobs, which is the source of most confusion. In the dog's bowl it signals a relationship that used to be shown by an ending on the noun itself; in don't it stands where letters have been dropped, since the phrase began as do not. The mark came into printing as an elision sign.

Because the possessive sense no longer depends on any spoken ending, writers guess where it belongs, and errors spread: its and it's swap places, and plural signs get an apostrophe they do not need. Style guides have argued about names ending in s for over a century, and the rule remains more convention than logic.

Where this entry sits

This category gathers small surprises about the English language, from odd spelling rules to words that quietly hide their own history. Expect palindromes, punctuation oddities, borrowed terms, and the strange ways writing systems record spoken speech. The full list sits on the Words and Language page, where every entry is listed in order.