Why do some adjectives need a preposition?

Because the adjective is incomplete without a slot for the thing it relates to. Interested needs a subject (interested in otters), good needs a skill (good at reading the water), afraid needs a feared thing (afraid of the loose planks). English fills that slot with a fixed preposition plus a noun or -ing. The preposition is part of the adjective's grammar, not a free choice.

Do I use -ing or a to-infinitive after an adjective with a preposition?

Use -ing (or a noun). A preposition cannot be followed by a to-infinitive: good at spotting, afraid of slipping, responsible for locking, interested in watching. The to-infinitive belongs to a different set of adjectives that have no preposition: happy to wait, ready to leave, likely to flood.

What are the most common adjective-preposition pairs?

Good at, bad at, interested in, involved in, afraid of, proud of, tired of, famous for, responsible for, similar to, used to, keen on, pleased with, angry with, worried about, excited about. Learn them as chunks. A dictionary entry that lists the preposition after the adjective is the best check when you are unsure.

Is used to a preposition or a past form?

Both exist, and they are different. Be used to plus a noun or -ing means accustomed: The warden is used to wet boots. Used to plus a bare verb means a past habit: The warden used to volunteer on Sundays. If be is in the sentence, to is a preposition and -ing follows.

Can I say interested to or keen to?

Interested to is not the standard pair; use interested in plus a noun or -ing: interested in watching the otter run. Keen to plus an infinitive is fine for an eager action (She is keen to start at dawn), but the hobby pair is keen on: keen on birdwatching. Do not put -ing after keen to, and do not put a to-infinitive after keen on.

English grammar · Intermediate

Adjectives with Prepositions: Good At, Interested In, Afraid Of

Written by Eleanor Whitfield, Lead English Curriculum Editor · Reviewed September 2026

Many English adjectives take a fixed preposition before a noun or an -ing form: good at drawing, interested in otters, afraid of heights, famous for kingfishers, similar to the last brood, keen on birdwatching. The preposition belongs to the adjective, not to the noun, and it does not change. After most of these adjectives you cannot switch to a to-infinitive (*interested to otters); a smaller set (happy to, ready to, likely to) does take the infinitive, and those are the exception, not the rule.

Priya is keen on otters and famous for the sketches she makes from the hide.

keen on and famous for: each adjective locks in its own preposition

What it is

An adjective can describe on its own (The boardwalk is wet). A large set of adjectives, though, are incomplete until a preposition opens a slot for a noun or an -ing form: good at spotting herons, interested in the otter run, afraid of the loose planks. The pair is learned as a chunk because the preposition is not guessable from meaning: you are good at a skill, not good in it, and you are famous for a result, not famous of it. After the preposition, English wants a noun (afraid of heights) or an -ing form (afraid of slipping). A to-infinitive in that slot is the usual error, except with a short list of adjectives that never took a preposition in the first place (happy to wait, ready to leave).

She is good at reading the water. (good at + -ing) She is interested in otters. (interested in + noun) She is happy to wait in the hide. (happy + to-infinitive, no preposition)

How to spot it

Look for an adjective followed by at, of, in, for, to, with, about, from, or on, then a noun or an -ing form. If you can drop the preposition and the sentence still works with a to-infinitive (ready to leave), you are in the exception set. If dropping the preposition ruins the sentence (interested otters), the preposition is required.

Ewan is good at reading the water from the hide. (good at plus -ing)
Priya is interested in the otter run at dusk. (interested in plus a noun phrase)
The reserve is famous for its kingfishers. (famous for plus a noun)
This brood is similar to the one on the far bank. (similar to plus a noun)

To after similar, used, married, and close is a preposition (similar to the last brood), so a noun or -ing follows, not a bare verb. To after happy, ready, and likely is the infinitive marker (happy to wait).

Adjectives with Prepositions Quick Reference

Common adjective plus preposition groups

Preposition	Typical adjectives	Example
at	good, bad, skilled, surprised	good at spotting herons
in	interested, involved, absorbed	interested in the otter run
of	afraid, proud, jealous, tired, capable, full	afraid of the loose planks
for	famous, responsible, known, suitable	famous for kingfishers
to	similar, used, married, close, allergic	similar to the last brood
on	keen, dependent, based	keen on birdwatching
with	pleased, angry, bored, satisfied	pleased with the sketches
about	worried, excited, sorry, sure	worried about the water level

Common Adjectives with Prepositions Examples in English

Grouped by the preposition the adjective locks in, which is how these combinations are stored:

At, In, and On

Ewan is good at reading the water from the hide.: good at plus a skill in -ing
Priya is interested in the otter run at dusk.: interested in plus a noun
The volunteers are involved in counting the herons.: involved in plus -ing
She is keen on birdwatching along the boardwalk.: keen on plus -ing

Good at a skill, interested in a subject, keen on a hobby. At, in, and on are not interchangeable here.

Of and For

He is afraid of the loose planks on the boardwalk.: afraid of plus a noun
Priya is proud of the sketches she made from the hide.: proud of plus a noun phrase
The reserve is famous for its kingfishers.: famous for a notable feature
Soren is responsible for locking the hide at dusk.: responsible for plus -ing

Of often follows a feeling about something (afraid, proud, tired). For often follows a cause or a duty (famous for, responsible for).

To, With, and About

This brood is similar to the one on the far bank.: similar to: to is a preposition here
The warden is used to wet boots on the boardwalk.: used to plus a noun, not the used-to past
Ewan was pleased with the sketches.: pleased with a thing
They are worried about the water level in the reedbed.: worried about a situation

Used to plus a noun or -ing means accustomed. Used to plus a bare verb (She used to volunteer) is a different structure, a past habit.

Preposition Plus -ing, Not Infinitive

She is good at spotting herons from the hide.: -ing after the preposition
He is afraid of slipping on the wet planks.: afraid of plus -ing
They are tired of waiting for the otter run.: tired of plus -ing
Priya is capable of sitting still for an hour.: capable of plus -ing

A preposition cannot be followed by a to-infinitive or a bare verb. After at, of, in, for, on, the next verb is always -ing.

How Adjectives with Prepositions Work

The preposition is part of the adjective. What follows it is a noun phrase or an -ing form.

Learn the Adjective and the Preposition as One Chunk

The preposition is not chosen by logic in each sentence. Good takes at, interested takes in, afraid takes of, famous takes for, similar takes to, keen takes on. Swapping them (good in drawing, interested at otters) is the error. The reliable method is to store the pair: good at, interested in, afraid of. Dictionaries list the preposition after the adjective for this reason.

She is good at reading the water, not good in reading the water.

good at is the stored pair

Store the pair: adjective + preposition.

After the Preposition: Noun or -ing

A preposition is followed by a noun, a pronoun, or an -ing form: interested in otters, interested in them, interested in watching the otter run. It is not followed by a to-infinitive (*interested to watch) or a bare verb (*interested watch). That is the same rule as any other preposition in English, applied to this adjective slot.

He is afraid of the loose planks. He is afraid of slipping.

of plus a noun, or of plus -ing

Preposition, then a noun or -ing.

The Object of the Preposition Can Be a Clause with -ing

When the thing you are good at, afraid of, or responsible for is an action, English turns that action into -ing: good at spotting, responsible for locking, tired of waiting. The -ing form can take its own object (spotting herons, locking the hide). It still sits in the noun slot after the preposition.

Soren is responsible for locking the hide at dusk.

for plus -ing plus the object of that -ing

An action after the preposition becomes -ing.

Some Adjectives Take Different Prepositions for Different Meanings

Good at is a skill; good for is a benefit (Rain is good for the reedbed). Angry with a person, angry about a situation. Sorry for a person you pity, sorry about a mistake. The adjective stays the same; the preposition picks the meaning. When two prepositions are possible, they are not free variants.

She is good at sketches. Rain is good for the reedbed.

good at a skill vs. good for a benefit

A new preposition can mean a new sense.

Common Mistakes with Adjectives with Prepositions

Incorrect: Priya is interested to watch the otter run.

Correct: Priya is interested in watching the otter run.

Interested takes the preposition in, and a preposition is followed by a noun or -ing, not a to-infinitive. Interested to is a common mix of this pattern with happy to.

Incorrect: Ewan is good in reading the water.

Correct: Ewan is good at reading the water.

The skill pair is good at, not good in. In appears with interested in and involved in. Each adjective keeps its own preposition.

Incorrect: The warden is used to lock the hide at dusk.

Correct: The warden is used to locking the hide at dusk. / The warden used to lock the hide at dusk.

Be used to (accustomed) takes a noun or -ing because to is a preposition. Used to (past habit) takes a bare verb and has no be. The two sentences mean different things; pick the one you want and keep its grammar.

Incorrect: She is keen to birdwatching along the boardwalk.

Correct: She is keen on birdwatching along the boardwalk.

Keen takes on plus a noun or -ing in this meaning. Keen to plus an infinitive exists (She is keen to start at dawn) but it cannot be followed by an -ing noun. Do not mix on with to.

Adjectives that Take a To-Infinitive Instead

A short list never needed a preposition, and a few adjectives do both jobs.

Happy, ready, likely, easy, glad

These take a to-infinitive, not a preposition: happy to wait, ready to leave, likely to flood, easy to spot, glad to help.

Priya is happy to wait in the hide until dusk.: happy to plus infinitive
The boardwalk is likely to flood after heavy rain.: likely to plus infinitive
Kingfishers are easy to spot from the far bank.: easy to plus infinitive

Easy, difficult, and possible often appear in it-patterns: It is easy to spot them from the far bank.

Afraid, sure, certain: both patterns

Afraid of plus a noun/-ing names a feared thing. Afraid to plus an infinitive names an act the person will not do. Sure of / sure about vs. sure to split in a similar way.

He is afraid of dogs on the path.: afraid of a noun: the feared thing
He is afraid to take the short cut after dark.: afraid to: he will not do it
The water is sure to rise tonight.: sure to: a confident prediction, infinitive

When both exist, of/about looks at a noun situation and to looks at an action.

Good at vs. good to / good for

Good at is a skill. Good for is a benefit. Good to plus a person (good to visitors) describes treatment; good to plus a verb is less common than easy to.

Ewan is good at reading the water.: good at a skill
Rain is good for the reedbed.: good for a benefit
The wardens are good to volunteer sketchers.: good to a person: kind towards them

Good in is not the skill pair in standard English. Store good at.

Quick Check: Adjectives with Prepositions

Add the missing preposition, or choose -ing vs. infinitive.

1. Priya is interested ___ the otter run at dusk.

Answer: in

interested in

2. Ewan is good ___ reading the water from the hide.

Answer: at

good at a skill

3. He is afraid ___ slipping on the wet planks.

Answer: of

afraid of plus -ing

4. The reserve is famous ___ its kingfishers.

Answer: for

famous for a notable feature

5. She is happy ___ wait in the hide until dusk. (to / on / of)

Answer: to

happy takes a to-infinitive, no preposition

6. The warden is used to ___ (lock) the hide at dusk. (accustomed)

Answer: locking

be used to plus -ing

Adjectives with Prepositions FAQs

Why do some adjectives need a preposition?: Because the adjective is incomplete without a slot for the thing it relates to. Interested needs a subject (interested in otters), good needs a skill (good at reading the water), afraid needs a feared thing (afraid of the loose planks). English fills that slot with a fixed preposition plus a noun or -ing. The preposition is part of the adjective's grammar, not a free choice.
Do I use -ing or a to-infinitive after an adjective with a preposition?: Use -ing (or a noun). A preposition cannot be followed by a to-infinitive: good at spotting, afraid of slipping, responsible for locking, interested in watching. The to-infinitive belongs to a different set of adjectives that have no preposition: happy to wait, ready to leave, likely to flood.
What are the most common adjective-preposition pairs?: Good at, bad at, interested in, involved in, afraid of, proud of, tired of, famous for, responsible for, similar to, used to, keen on, pleased with, angry with, worried about, excited about. Learn them as chunks. A dictionary entry that lists the preposition after the adjective is the best check when you are unsure.
Is used to a preposition or a past form?: Both exist, and they are different. Be used to plus a noun or -ing means accustomed: The warden is used to wet boots. Used to plus a bare verb means a past habit: The warden used to volunteer on Sundays. If be is in the sentence, to is a preposition and -ing follows.
Can I say interested to or keen to?: Interested to is not the standard pair; use interested in plus a noun or -ing: interested in watching the otter run. Keen to plus an infinitive is fine for an eager action (She is keen to start at dawn), but the hobby pair is keen on: keen on birdwatching. Do not put -ing after keen to, and do not put a to-infinitive after keen on.