Why Prepositions in Idioms Don't Follow "Normal" Rules

Most of the time, you can guess a preposition by thinking about its basic meaning — on the table, in the box, at the door. But English is full of fixed expressions where the preposition doesn't follow logic. You simply have to learn the whole phrase as a unit, the way you'd learn a single vocabulary word.

Take the expression by accident. There's no spatial or directional reason for by here — it's just the preposition English locked into centuries ago. If you try to reason it out, you might reach for on accident or with accident, and both sound wrong to a native ear (though on accident is creeping into informal American English, it's still considered non-standard in most contexts).

The practical rule: when a preposition is part of an idiomatic expression, treat the whole phrase as one item. Don't swap the preposition based on translation from your language.

Worked Examples

Consider these two sentences:

✅ She succeeded in convincing the whole team. ❌ She succeeded to convincing the whole team.

Many learners write succeeded to because in their first language the equivalent verb takes something like "to." But in English, succeed always pairs with in when followed by an action.

Here's another:

✅ He insisted on paying for dinner. ❌ He insisted in paying for dinner.

Spanish and Portuguese speakers especially fall into this trap, because insistir en maps onto in in their minds. English wants insist on.

One more, because this one catches almost everyone:

✅ I'm not used to waking up early. ❌ I'm not used of waking up early.

Be used to (meaning "be accustomed to") is a fixed combination. The to here is a preposition, not part of an infinitive — that's why a gerund (waking) follows it, not a bare verb.

Expressions That Look Alike but Aren't

Some idioms differ by just one preposition, and the meaning shifts completely:

• in time = early enough ("We arrived in time for the opening.")

• on time = at the scheduled moment ("The train left on time.")

• by the way = incidentally, introducing a side topic

• in the way = blocking, obstructing ("Your suitcase is in the way.")

Mixing these up doesn't just sound odd — it changes what you're saying. A learner who writes "Don't worry, we'll get there in time" is saying something genuinely different from "we'll get there on time," and both are correct English — just not interchangeable.

The Mistake B1–B2 Learners Make Most

The single biggest error at this level is translating the preposition directly from your native language. French speakers write depend of (from dépendre de) instead of depend on. German speakers write wait on (from warten auf) instead of wait for. Arabic speakers write afraid from instead of afraid of.

The fix isn't a grammar rule — it's a study habit. Every time you learn a new verb or adjective that takes a preposition, write down the whole chunk: apologize for, consist of, interested in, responsible for, good at. Quiz yourself on the preposition, not just the main word.

A short list of expressions that trip up learners at this level, worth memorizing outright:

• on purpose (not by purpose or with purpose)
• for a change (not to a change)
• at risk (not in risk)
• in charge of (not in charge for)
• by heart (not from heart or by the heart)

If you get the preposition wrong in one of these, a native speaker will still understand you — but it immediately marks the sentence as non-native. Getting them right is one of the fastest ways to sound more natural.