Apostrophes: Apostrophes are used to indicate possession--"Professor Lupton's lecture" or "Odysseus' courage." The "lecture" belongs to "Professor Lupton" and the "courage" belongs to "Odysseus." With singular nouns possession is shown by adding apostrophe plus s. With plural nouns or nouns, like "Odysseus," that already end in -s, the apostrophe follows the final s.
For more complicated situations consult Writing from A to Z.

An important exception: The most frequently made mistake is to confuse its (with no apostrophe) and it's (with an apostrophe). Its, without the apostrophe, is possessive, an exception to the general rule. It's, with the apostrophe, is the contraction for it is.

 RETURN TO GRAMMAR CHECKLIST