Sometimes, grammar errors in SAT writing multiple choice questions aren’t rule-based. That is, there are errors in sentences that have nothing to do with what you might’ve learned in an English class. In order to get them right, you have to just know the answer. It’s all about your ear. Ask yourself, “does that sound right?”
This might be the only time in SAT writing multiple choice that I say to go with your gut about an error. Most times, you should be trying to find why something is wrong as it’s written.
But when it’s a preposition that’s underlined, it’s all about your ear.
Idioms and prepositions
You might see prepositions lumped under the category of “idiom” in SAT prep material. That’s not technically wrong, but it’s misleading. Usually, when we say “idiom,” we mean a metaphorical expression or phrasal verb—like “bite the dust” or “cracking up”—that doesn’t convey a clear meaning just from the words we use. Think of how it’d sound to a non-native speaker.
The SAT doesn’t care about that kind of idiom. Instead, the test-makers want to know if you can choose the right preposition to go with words which actually do carry the meaning they’re expected to. For instance, you might disagree with an idea, but you can’t object with it. Instead, you object to it. Both “disagree” and “object” mean exactly what we expect them to in those phrases. It’s only the preposition that’s weird.
How to answer preposition questions
During your SAT, if you see an underlined preposition, find the words before and/or after that should get paired with it. Pretty often, that means finding the verb or adjective that came before the preposition, like in the “disagree” vs. “object” example above, but sometimes it’s about the words after the preposition, instead.
In the sentence “I’m on my classmate’s phone,” you’d note the word “phone,” and ask whether “on” and “phone” link well together, which they do. Similarly, an actor might appear in a movie, on TV, or at a restaurant. In those cases, it’s not about the word “appear,” but about “movie,” “TV,” and “restaurant.”
Whether it’s the word before or after the preposition, you have to find that related word. Then, it’s all about your ear.