to + Infinitive

F. To + Infinitive Forms: The infinitive of a verb has two forms: the "to-infinitive" and the infinitive without "to".
a. The to-form consists of "to" plus the base form of the verb. (e.g. We came here to work, not to play.)
b. The form without to consists of the base form of the verb. (e.g. She made us wait for half an hour.)
c. The negative infinitive is formed by putting "not" in front of any form of the infinitive ("not to ~"). (e.g. He asked me not to be late.)

F1. Function of the To-Infinitive: The to-infinitive is used in many sentence constructions, often expressing the purpose of something or someone's opinion about something.
a. to indicate the purpose or intention of an action. In this case to has the same meaning as in order to or so as to. (e.g. I am calling to ask you about dad.)
b. as the subject of the sentence. (e.g. To be or not to be, that is the question.)
c. to indicate what something can or will be used for. In this pattern, the to-infinitive follows a noun or pronoun. (e.g. Would you like something to drink?)

F2. use the to-infinitive: to express ‘purpose’. (e.g. He bought some flowers to give to his wife.)
a. We sometimes say ‘in order to’ or ‘in order not to’. (e.g. We set off early in order to avoid the traffic.)
b. or we can say ‘so as to’ or ‘so as not to’. (e.g. We set off early so as to avoid the traffic.)
c. some verbs are followed by a direct object and the infinitive: advise, ask, encourage, invite, order, persuade, remind, tell, warn, expect, intend, would prefer, want, would like (e.g. She reminded me to turn the lights out.)

F3. Sometimes the to-infinitive gives a reason for the adjective:
a. disappointed, glad, sad, happy, anxious, pleased, surprised, proud, unhappy (e.g. We were happy to come to the end of our journey = We were happy because we had come to the end of our journey), and other adjectives with the "to-infinitive" are: able, unable, due, eager, keen, likely, unlikely, ready, prepared, unwilling, willing (e.g. Unfortunately I was unable to work for over a week.)

b. often use the "to-infinitive" with these adjectives after it to give opinions: difficult, easy, possible, impossible, hard, right, wrong, kind, nice, clever, silly, foolish (e.g. It’s easy to play the piano, but it’s very difficult to play well.)

F4. Some verbs are followed by the "to-infinitive". 
a. verbs of thinking and feeling: choose, decide, expect, forget, hate, hope, intend, learn, like, love, mean, plan, prefer, remember, want, would like, would love, etc.(e.g. I decided to go home as soon as possible.)
b. verbs of saying: agree, promise, refuse, etc. (e.g. They agreed to start a business together.)
c. other common verbs are: arrange, attempt, fail, help, manage, tend, try, want, and offer, deserve, afford, threaten, etc.
d. also use 'to ~' after seem, appear, tend, pretend, claim (e.g. They seem to have plenty of money.) There is also a continuous infinitive (to be doing) and a perfect infinitive (to have done) (e.g. I pretended to be reading the newspaper. (= I pretended that I was reading))
e. Verbs are followed by to ~ (infinitive). (e.g. We expected to be late. (verb + to ~). We expected Dan to be late. (Verb + object + to)) Do not say 'want that' (e.g. Do you want me to come with you? (not Do you want that I come?))
f. After help, can use the infinitive with or without to. (e.g. Can you help me to move this table? or Can you help me move this table?)

F5. Other use the "to-infinitive"
a. use the preposition "for" to show who these adjectives refer to: difficult, easy, possible, impossible, hard (e.g. It was difficult for us to hear what she was saying.) U
se the preposition "of" with other adjectives. (e.g. It’s kind of you to help.)
b. As a postmodifier after abstract nouns like: ability, desire, need, wish, attempt, failure, opportunity, chance, intention. (e.g. I have no desire to be rich.) We often use a to-infinitive as a postmodifier after an indefinite pronoun. (e.g. When I am travelling I always take something to read.)
c. After dare, can use the infinitive with or without to. (e.g. I wouldn't dare to tell him. Or I wouldn't dare tell him.) But after dare not (or daren't), you must use the infinitive without to. (e.g. I daren't tell him what happened. (not I daren't to tell him)
d
. After some verbs, can use a question word (what/ whether/ how etc.) + 'to ~'. We use this structure especially after: ask, decide, know, remember, forget, explain, learn, understand, wonder (e.g. We asked how to get to the station.)
e. Also show/ tell/ ask/ advise/ teach somebody what/ how/ where to do something. (e.g. Can somebody show me how to change the film in this camera?)

F6. Verbs have the structure verb + object = to ~: tell, order, remind, warn, force, invite, encourage, persuade, teach, get (= persuade, arrange for), enable. (e.g. Can you remind me to phone Sam tomorrow?)
a. Passive verb: I was warned not to touch the switch.
b. After advise, recommend and allow, two structure are possible. (e.g. I wouldn't advise/ recommend staying in that hotel. (verb + -ing (without an object)) I wouldn't advise/ recommend anybody to stay in that hotel. (Verb + object + to ~). With (be) allowed (passive): Parking isn't allowed in front of the building.
c. Verbs (make, let) have the structure verb + object = infinitive (without to) (e.g. I made him promise that he wouldn't tell anybody what happened. (not to promise))
d. say 'make somebody do' (not to do), but the passive is '(be) made to do' (with to) (e.g. We were made to wait to wait for two hours. (= They made us wait ~))

F7. Some verbs are followed by a noun and the 'to-infinitive'. (e.g. She asked him to send her a text message.) Common verbs with this pattern are:
a. verbs of saying: advise, ask, encourage, invite, order, persuade, remind, tell, warn (The verb warn is normally used with not), etc. (e.g. The police warned everyone not to drive too fast.)
b. verbs of wanting or liking: expect, intend, would prefer, want, would like, etc.
c. other verbs with this pattern are: allow, enable, force, get, teach, etc.
d. Many of these verbs are sometimes followed by a Passive Infinitive (to be + past participle). (e.g. I expected to be met when I arrived at the station.)

F8. after some verbs 'to ~' is not possible: enjoy, think, suggest, etc. (e.g. I enjoy reading. (not enjoy to read)).
a. We cannot use suggest with the structure verb + object + to ~. (e.g. Jane suggested that I should ask your advice. (not Jane suggested me to ask))

more about the Gerund (-ing) and to ~ (infinitive)

Be/ get used to something

F9. I'm used to something = it is not new or strange for me. (e.g. Tom lives alone. He doesn't mind this because he has lived alone for 15 years. It is not strange for him. He is used to it. He is used to living alone.)
a. After be/ get used, we cannot use the infinitive (to do/ to drive etc.). (e.g. She is used to driving on the left. (not She is used to drive)
b. When we say 'I am used to something', to is a preposition, not a part of the infinitive. (e.g. Tom is used to living alone. (not Tom is used to live))
c. I am used to (doing) something = it is not strange or new for me. (e.g. I am used to the weather in this country.) vs. I used to do something = I did it regularly in the past but no longer do it.) We can use this only for the past, not for the present. (e.g. I used to drive to work every day, but these days I usually go by bike.)

more about the Gerund (-ing) and to ~ (infinitive)