to express purpose

after certain verbs (agree, appear, decide, expect, hope, plan, promise, refuse, etc.)

after would like, would prefer, would love, etc. to express specific preference

after adjectives which describe feelings/emotions (happy, sad, glad etc.), willingness/unwillingness (willing, eager, reluctant and the adjectives lucky and fortunate

after too / enough

to talk about an unexpected event, usually with only

with it + be + adjective/noun

after be + first/second/next/last...

after ask, learn, explain, decide, find out, want, want to know, etc. when they are followed by a question word

after modal verbs

after let, make, see, hear and feel

NOTE: after be made, be heard, be seen etc. (passive form) we use to-infinitive:

He was made to throw his cigarette.

after had better and would rather

help can be followed either by to-infinitive or infinitive without to

Present (to) play refers to the present or future.

Present Continuous (to) be playing expresses an action happening now.

Perfect (to) have played is used to show that the action of the infinitive happened before the action of the verb.

Perfect Continuous (to) have been playing is used to emphasise the duration of the action of the infinitive, which happened before tha main verb.

as a noun

after certain verbs admit, appreciate, avoid, continue, deny, fancy go (for activities), imagine, mind, miss, qiut, save, suggest, practise, consider, prevent

after love, like, enjoy, prefer, dislike, hate to express general preference

after expressions be busy, it’s no use, it’s (no) good, it’s (not) worth, what’s the use of, can’t help, there’s no point in, can’t stand, have difficulty (in), have trouble etc.

after spend, waste or lose

after to with look forward to, be used to, in addition to, object to, prefer (doing sth to sth else)

after other prepositions

after hear, liste to, notice, see, watch and feel to describe an incomplete action

BUT: We use the infinitive without to to describe the complete actionI heard Maria tell the story. (I heard the whole story.)

remember not recall

He forgot to post the letter.

I’ll never forget visiting the Taj Mahal.

not forget recall

Did you remember to feed the cat?

I remember telling him to lock all the doors.

intend to involve

I’m sorry, I never meant to hurt your feelings.

Passing an exam means studying hard.

be sorry to (normally used in the present simple with say, tell, inform) feel sorry about

We regret to inform you that you have failed your exams.

I regret speaking to her so rudely.

do one’s best, attempt do sth. as experience

He tried to call but the line was busy.

Why don’t you try taking some vitamins?

stop briefly to do sth. else finish, give up

He stopped to buy a newspaper on his way to work.

He stopped eating junk food so as not to gain weight.