We use gerunds (verb + ing):
- After certain verbs – I enjoy singing
- After prepositions – I drank a cup of coffee before leaving
- As the subject or object of a sentence – Swimming is good exercise
We use ‘to’ + infinitive:
- After certain verbs – We decided to leave
- After many adjectives – It’s difficult to get up early
- – I came to London to study English
We use the bare infinitive (the infinitive without ‘to’):
- After modal verbs – I can meet you at six o’clock
- After ‘let’, ‘make’ and (sometimes) ‘help’ – The teacher let us leave early
- After some verbs of perception (see, watch, hear, notice, feel, sense) – I watched her walk away
- After expressions with ‘why’ – why go out the night before an exam?