"I'm interested on photography."

Close, but no. It's "interested in photography." And before you ask why - there isn't really a why. The preposition that follows an adjective in English is fixed by the adjective itself, the way a key is fixed to a lock. You don't get to pick.

The good news? There aren't that many of these pairs, and once you memorize them as units (not as two separate words), they stop being a problem forever.

Quick Answer

• Many English adjectives come permanently attached to a specific preposition.
• The preposition is not optional and not negotiable - it's baked into the phrase.
• Best strategy: learn "good at," "afraid of," "married to" as single chunks, not as adjective + random preposition.

The Simple Rule

• Treat adjective + preposition as one unit, like a verb tense.
• When the preposition is followed by a verb, that verb takes the -ing form: "I'm good at cooking", not "to cook."
• "Used to" is the famous trap: "I'm used to working late" (familiar with it) vs "I used to work late" (past habit, no preposition).

Natural Examples

Skills and ability

• She's really good at chess.
• I'm bad at remembering names - sorry, what was yours again?
• He's terrible at keeping secrets.

Feelings and interests

• My brother is interested in astronomy.
• I'm afraid of spiders, even tiny ones.
• We're excited about the trip next week.
• She's worried about the deadline.
• He's proud of his daughter's results.

Relationships and similarity

• This phone is very similar to the older model.
• My answer is completely different from yours.
• She's been married to Daniel for ten years.
• He's not very familiar with the new software.

State and condition

• The room was full of people.
• I'm responsible for the morning report.
• She's kind to animals.
• Sugar is bad for your teeth, but cookies are good for the soul.

The special case: "used to"

• I'm used to waking up early. (Familiar with it; verb takes -ing.)
• I used to wake up early. (Past habit; no preposition; base verb.)

These two look identical but mean completely different things. If "be" appears before "used to," it's the preposition version and the next verb gets -ing.

Common Mistakes

• ❌ "I'm interested on cooking." → ✅ "I'm interested in cooking." · "Interested" only ever pairs with "in," never "on" or "about."
• ❌ "She's married with a doctor." → ✅ "She's married to a doctor." · In English you're married to a person; "married with" usually means "married and also has," e.g. "married with two kids."
• ❌ "He's afraid from dogs." → ✅ "He's afraid of dogs." · "Afraid" always takes "of," never "from."
• ❌ "I'm used to wake up early." → ✅ "I'm used to waking up early." · After "be used to," the next verb must be -ing form because "to" is a preposition here, not the infinitive marker.
• ❌ "This is similar with that one." → ✅ "This is similar to that one." · "Similar" takes "to." "Compared with" exists, but "similar to" is the fixed pair.
• ❌ "I'm responsible of the project." → ✅ "I'm responsible for the project." · "Responsible" always pairs with "for."

Exam Trap

In TOEIC Part 5, TOEFL Structure-style sentence completion, and IELTS writing rubrics, adjective + preposition pairs are a favourite testing point because there's almost no logic to fall back on - you either know the pair or you don't. The classic trap is offering you four plausible-sounding prepositions ("of / for / in / about") where only one is the fixed partner. The other trap is the "used to" / "be used to" distinction, which examiners use to test whether you understand that "to" is sometimes a preposition (so the next verb is -ing) and sometimes part of an infinitive (so the next verb is base form). When in doubt, ask yourself: is "be" in front of "used to"? If yes, the next verb is -ing.

Mini Practice

1. She's very good _____ playing the violin.
2. I'm not familiar _____ this part of town.
3. He's afraid _____ flying, so he always takes the train.
4. I'm used _____ (drive) on the left now.
5. They're very proud _____ their new home.

Answer Key

1. at - "Good at" is the fixed pair for describing skills and abilities.
2. with - "Familiar with" is the standard collocation when describing knowledge of something.
3. of - "Afraid of" is the only correct preposition here; "from" and "about" don't pair with "afraid."
4. to driving - "Be used to" needs the -ing form because "to" is a preposition, not the infinitive marker.
5. of - "Proud of" is the locked pair when expressing pride in someone or something.

Tiny Summary

Don't try to figure out why these prepositions go with these adjectives - they just do. Memorize them as inseparable two-word units and your English will instantly sound less like a textbook and more like a person.