Ha, ha, ha! That’s a good joke!

O used as a vocative or to express a desire or imprecation does not call for an exclamation.

O John.

Oh, yes.

O, that night would come!

The exclamation is sometimes used in job printing to fill out a display line or for other inadequate reasons. These uses should be avoided.


THE APOSTROPHE

The apostrophe is primarily the sign of the possessive case, but it has several other uses.