The infinitive consists of "to+ verb prototype" and its negative form is "not to+ verb prototype". An infinitive can take an object or an adverbial to form an infinitive phrase. The person and number have not changed, but the tense and voice have changed. The infinitive can be used as subject, object, adverbial, predicative and attributive, but it cannot be used as predicate alone. The logical subject of infinitives sometimes consists of "for+ nouns or pronouns".
The usage of infinitive.
1) as the subject. When the infinitive phrase is used as the subject, it is often placed after the predicate as the formal object. For example:
I'll believe that when I see it.
It is right to give up smoking.
2) as an object. When an infinitive phrase is used as an object, if there is an object complement, the infinitive object is often placed after the object complement as a formal object. For example:
He wants to go.
I find it interesting to study history.
Some verbs can only be followed by infinitives and must be followed by gerunds. Such as: decision, plan, desire, expectation, hope, wish, pretend, promise, rejection, burden, consent, request, failure, tendency, pretend, management.
3) as an object complement. For example:
He asked me to do the work with him.
Note: In the complement after feeling, hearing, noticing, observing, seeing, watching, owning, making, etc. The infinitive is not used. However, if these sentences become passive structures, they must be adopted. For example:
I often hear him sing this song.
People often hear him sing this song.
Note: When the infinitive follows the preposition but, if there are various forms of action verbs do in front of the preposition, then the infinitive behind these prepositions will not take to, otherwise it will take to. In addition, you can't choose but and you can't omit the infinitive after to. For example:
She can do nothing but cry.
I have no choice but to go.
4) As an attribute. For example:
I have some books to show you.
If the infinitive used as an attribute is an intransitive verb, or the noun or pronoun modified by the infinitive is the place and tool of the infinitive action, then there must be a corresponding preposition after the infinitive. For example:
He is looking for a room to live in.
There is nothing to worry about.
Please give me a knife to cut things.
But if the noun modified by the infinitive is time, place or way, the preposition after the infinitive is customarily omitted. For example:
He has no money and no place to live.
(2) When the noun or pronoun modified by the infinitive is the receiver of the infinitive action, the infinitive can be used in both the active voice and the passive voice, but its meaning is different. Try to compare:
Do you have anything to send?
Do you have anything to send? The actor who wants to send the infinitive is "you")
Do you have a seat?
Do you have anything to send (to me or others)? Is the infinitive actor "me" or "someone else"]
5) as an adverbial, indicating the purpose, reason, result or condition. For example:
I came to see you. (purpose)
We are very excited to hear the news.
He hurried to the school and found no one there. (result)
Look at him, and you will like him. (conditions)
The adverbial of purpose can also mean for or so for, but so it can't be placed at the beginning of the sentence. For example:
He worked very hard to pass the exam.
We ran all the way so as not to be late.
After adjectives are used as predicative, infinitives can also be used as adverbials. For example:
I'm glad to hear the news.
This question is difficult to answer.
"Tai+adjective or adverb+infinitive" as adverbial. For example:
He is too old to do that.
In addition, infinitives are often used as adverbials when there is the word enough in a sentence. For example:
This room is big enough to accommodate us.
6) as a predicative. For example:
My job is to help patients.
7) As an independent component. For example:
To be honest, I don't agree with you.
8) infinitives are used with interrogative words who, which, when, where, how, what, etc. You can be a noun, a subject, a predicate and an object in a sentence. For example:
He doesn't know what to say. (object)
How to solve the problem is very important. (theme)
Note: when used with why, it is only used in short questions that begin with why or why not, and the infinitive after it is unnecessary. For example:
Why not have a rest?
9) Whether the infinitive in a sentence is active or passive is easy to judge in most cases, but sometimes it is really complicated. Please note the following points:
① When nouns or pronouns modified by infinitives and infinitives logically form a subject-predicate relationship, infinitives often use active forms. For example:
Do you have a key to open the door?
A key opens the door. )
② When the infinitive forms a logical verb-object relationship with the noun or pronoun modified before and a logical subject-predicate relationship with the subject of the sentence, the infinitive usually uses the active form.
I have a letter to write. I write letters. )
He needs a room to live. He lives in a room. )
I know what to do. What do I do? )
But if this sentence is changed to the following form, the infinitive can only be passive: I know what to do.
This is because what you want to do is an object clause, and the subject in the clause is the action object of the verb do.
When the infinitive is used as an adverbial of predicative adjectives and forms a logical verb-object relationship with the subject in the sentence, it is often used in the active form because people often think that adjectives are reserved for someone. For example:
It's difficult to talk to him. (talking to him)
This book is difficult to understand. (in order to understand this book)
In there be structure, when the speaker thinks that someone must finish something, the infinitive takes the active form; If the speaker emphasizes that the matter itself must be completed, use the passive form.
There is a lot of work to be done. Someone has to do the work. )
There is a lot of work to be done. The work has to be done. )
Please note that the following two sentences have different meanings:
There is nothing to do. I feel bored with nothing to do. )
There is nothing to do. Something is broken and can't be returned to normal. )
2. Tense of infinitive
The action represented by the general form of 1) infinitive usually occurs at the same time (or almost at the same time) or after the action (state) of the predicate. For example:
I saw him go out.
2) If the action (situation) indicated by the predicate has occurred and the action indicated by the infinitive is in progress, then the infinitive will use the progressive aspect. For example:
He pretended to be reading when she went in.
3) If the infinitive action occurs before the predicate verb, use the perfect form. For example:
I am sorry to have kept you waiting.
3. The voice of infinitive
When the logical subject of the infinitive is the receiver of the action represented by the infinitive, the infinitive usually uses the passive form. For example:
He asked to be sent to work in the countryside.
Our hopes may come true.
4. Reservation of infinitive symbols.
Sometimes, in order to avoid repetition, you can use to instead of infinitive, which often appears after the following verbs: expect, prefer, care, mean, forget, want, wish, hope, try, be glad/happy.
If there are be, have and have been in the omitted infinitive structure, these words should be kept. For example:
Are you on vacation?
No, but I want to be.
I didn't tell him the news.
Oh, you should have
I hope I can help you.