1. The forms and categories of the Infinitive. The use of ‘to’-Infinitive and the Bare Infinitive. ‘To’ without the Infinitive.

Principal Ideas: INF is the base form of the verb (dictionary entry for all verbal lexemes), thus it shares with the verbal class basic grammatical categories of Voice, Aspect and Time Correlation. In the sentence INF can be found with and without the distinctive particle TO. The particle can be used alone to represent the whole INF phrase. In the case of the so-called ‘split infinitive’ TO and INF can be separated by an inserted adverb.

1.1.1. Grammatical category of Voice: Active INF usually denotes an action whose performer is the subject (Subj.) of the sentence: I have work to do. Mary wants to become an artist. In some structures the subject of the INF is the Noun/Pronoun closely connected with it: Mother wants me to become an outstanding artist. Passive INF is used with the Subj. that names smb. or smth. undergoing the action of the INF: She ought to be told about it. I didn’t expect to be invited. After here/there + be phrase Pass. or Act. INF forms are used with little difference in meaning: There is a lot of work to do / to be done. Here are the names of people to invite / to be invited.

Note a certain difference in meaning in phrases there is something (anything, nothing) to do and there is something (anything, nothing) to be done: There’s nothing to do (= I’m bored, there’s no entertainment). There’s nothing to be done (=there’s no way of putting things right), e.g. There’s nothing to be done, the tape is spoilt, we’ll have to buy another one. The verb blame is often used in the active form of INF but with the passive meaning: Gregory is to blame for the broken window (Somebody will blame Gregory, he will be blamed).

1.1.2. Grammatical category of Aspect: Continuous INF is used for actions taking place at the time referred to in the Sentence: They happened at the moment to be standing near a small house. He seemed to be smoking a lot when he returned from his expedition. Non-Continuous INF doesn’t refer to particular time of the action, thus it is called Indefinite INF: His idea was to bring his new friend to our club meeting.

1.1.3. Grammatical category of Time Correlation: Perfect INF has the same kind of meaning as the Perfect Tenses, when they denote actions completed before other events or before some time: It’s good to have finished the work for the day (=It’s good when you have finished the work… or I’m pleased that I have finished the work…). Perfect INF is often used to talk about imaginary/planned actions, which were not completed (about things that didn’t happen): I meant to have phoned you, but I forgot. Perfect infinitives often follow the verbs seem and appear to speak about the result of observation and inference: We seem to have made a great mistake when we asked him to come. He appears to have missed his train. Perfect Continuous and Perfect Passive Infinitives are possible:

For about ten days we seemed to have been living on nothing but cold meat, cake and bread. Nothing seems to have been forgotten.

2. ‘to-INF’ is used after:

Adjectives	The game was exciting to watch. This box is not so heavy to carry alone.
Nouns or Pronouns	You will need something to eat. I will pack a book to read on the train.
Verbs except most of modal auxiliary verbs	She has decided to do a course in Geology. Do you promise to write to me every week?
Modal auxiliaries ought, have and be	Somebody has to do this job, after all. The opening of the monument was to be held on the first of the year. You ought to apologize.
Wh-Pronouns (what, who(m), where, which, why, when and how)	Can you show how to unlock this door? I’d like to know where to make my reservation for the trip. Fred hesitates whom to invite.
combinations V+Personal Object	I persuaded my boss to give me a pay rise. Nobody expected him to win.
Verbs of perception and causative verbs in the Passive in Predicative Complexes with INF and Compound Predicates	We were made to wait for Dr. Monroe (The secretary made us wait). In the square outside the public library an orchestra was heard to be playing jazz classics (We heard the orchestra play).
Note that the causative verb get requires a to-INF that follows	Get him to come to see me after lunch.

3. Bare INF (without ‘to’) is used:

After modal auxiliaries shall/should, will/would, can/could, may/might, must, need and dare	You may not leave your place until permission is granted. Could you tell me the time please? How dare you say that!
After verbs of sense perception (see, hear, feel, watch) and causative verbs (let, make, have, bid) in the Active Voice in Complex Object structures	I saw him run to the shop across the street. Nobody heard them enter the room. His words made me laugh. You hang the canvas up in a palm-tree and let the parrots criticize. Then they bade us depart.
After the verb help in AmE	Could you help me unload the car? (Compare the British Could you help me to unload…).
After modal phrases: had better, would rather, may just as well, can’t but, can do nothing (cannot do anything) but	I think I’d better make sure he is all right. One can’t but admire his sense of humour.
In subjectless Why-questions (rendering modal meaning) in which the INF is the only verbal element. Such use of INF often conveys the meaning “Why should you do something, that isn’t worth the trouble?”	Why worry? If you interfere you’ll never get the money; Why stand up if you can sit down?
In ‘Why-not’ suggestions that have the structure of questions	Why not begin at once? Why not wait till the winter sales to buy a new coat?

4. Particle ‘to’ is used alone to represent the whole INF phrase so that to economize on repeating words: Why didn’t you go to their farewell party? – I wasn’t invited to (=to come to the party). Will you join me for dinner? – I’d love to (=to join you). ‘To’ is dropped in subordinate clauses of Complex sentences after the verbs want and like when the clauses are introduced by what, where and other Wh-pronouns: You can do what you want (=what you want to do). You may say what you like, but I don’t believe you (…say what you like to say).

5. Split INF is an INF phrase in which ‘to’ is separated from INF by a modifying element, usually an adverb or please: My task is not to accuse or acquit; my task is to thoroughly investigate, to clearly define and to consistently systematize the facts. Split INF is not used very frequently, as it is stylistically rather strong, and should generally be avoided. There are cases when the split infinitive is the only way to avoid ambiguity: I have tried to consciously stop worrying about it.