Question: “Dear Grammar Guy, I debate with myself constantly about whether or not I am using ‘compose’ and ‘comprise’ correctly. Are they synonyms that can be used interchangeably, or should I only be using one in certain circumstances? Your help is much appreciated.”

Answer: This is a tough one, because they are so similar. Fortunately, there are guidelines that should help you out of this pickle.

“Compose” and “comprise” are both used to talk about the parts that make up a whole. The former means “to come together to form or make (something),” and the latter means “to be made up of (something)” or “to include or consist of (something).” Pay attention to the preposition “of” included in both definitions of “comprise” – it will be important later.

Merriam-Webster notes that “comprise” and “compose” have been used synonymously since the late 18th century – though not without complaints. “You should be aware,” it says, “that if you use [‘comprise’ and ‘compose’ synonymously] you may be subject to criticism for doing so.”

The trick to these two words is not so much in differentiating their meaning, but in knowing how to use each of them in a sentence. Here’s what you need to know:

• “Comprise” should fall between the whole and the parts, with the whole coming first. (ex. “America comprises 50 states and several territories.”)
• Avoid using “of” after “comprise” (even though, yes, it is technically standard English).
• “Compose” should follow the parts and lead into the whole. (ex. “Two dozen apples compose today’s harvest at the orchard.”)

There is some disagreement about whether “composed of” is proper English. After consulting several sources, I’m going to take this stand: You may use “composed of.” However, when you do so it creates a passive construction that functions the same as “comprise,” and should thus follow the whole and lead into the parts, like so: “America is composed of 50 states and several territories.”

Whew, complicated! Isn’t grammar fun, though?