What is a contraction?
A contraction is a shortened form of a word (or group of words) that omits certain letters or sounds. In most contractions, an apostrophe represents the missing letters. The most common contractions are made up of verbs, auxiliaries, or modals attached to other words: He would=He’d. I have=I’ve. They are=They’re. You cannot=You can’t.
Contractions are common in speech—so common that we don’t always take the time to pronounce them precisely, which leads to a particular contraction mistake writers might make if they’re not paying attention. In speech, we often pronounce could’ve, should’ve, and would’ve in a way that sounds identical to “could of,” “should of,” and “would of.” But you should never write could of, should of, or would of. Remember, could’ve, should’ve, and would’ve are contractions that mean could have, should have, and would have.
Some writers use less common contractions when they want to represent a particular style of speech. They might write somethin’ to represent the way people often don’t pronounce the final g of “something” in speech. Occasionally, you might see e’er (instead of ever) in poetry. And, of course, in the American South, you will probably encounter y’all (you all). Decade names are often contracted as well: the ’60s (the 1960s).
There are a few contractions, such as gonna (going to) and wanna (want to) that are written without apostrophes.
When to use contractions
Contractions are perfectly standard, but they’re usually considered to be relatively casual. If you’re writing something very formal, you may want to avoid using them except in cases like o’clock, where the full phrase (of the clock) truly is rare.