To comprise means to be made up of or to consist of certain parts. When we say “The United States comprises fifty states,” we mean those fifty states form or make up the whole country. When your teacher says “The reading list comprises ten books,” those ten books are what the list contains.

Think of comprise as a way to describe what ingredients go into something. A soccer team comprises eleven players. A dozen comprises twelve items. The solar system comprises the sun, eight planets, and various smaller objects like asteroids and comets.

Here's where people often get confused: comprise means “is made up of,” not “makes up.” You wouldn't say “Fifty states are comprised of the United States.” Instead, you'd say “The United States comprises fifty states” or “The United States is composed of fifty states.” The whole comprises the parts, not the other way around.

A helpful trick: you can usually replace comprise with “includes” or “consists of” and the sentence still makes sense. “The school library comprises thousands of books” works the same as “The school library consists of thousands of books.”