When is a noun not a noun?

Answer: when it’s an adjective.

One of the ACT’s favorite ways to play with you is to take words that normally act like nouns — often professions such as author, architect, scientist, etc. — and use them as adjectives. This might not seem like much of a big deal, or even something you’d really need to pay attention to, except that it actually involves something the ACT absolutely loves to test: commas.

Consider the following: You probably wouldn’t write something like “I.M. Pei is a celebrated, architect.” Even if you don’t know that “famous” is an adjective and that “architect” is a noun, you can probably feel that the comma is wrong there; there’s no natural break in the sentence.

But what about this?

Glass is perhaps the building material most often associated with celebrated architect, I.M. Pei.

Suddenly that comma seems like it could be ok. Perhaps you learned that you always put a comma before a person’s name.

Well, sometimes you do, but sometimes you don’t. And this is one of those cases in which you don’t.

The reason is that “architect,” in this case,” is being used to describe I.M. Pei. Even though “architect” looks like a noun, it’s acting as an adjective here. And since adjectives should never be separated from the nouns they describe by a comma, you do not need to place one between “architect” and “I.M. Pei.”