English verbs have three non-predicate forms: infinitive, gerund and participle. The person and number of non-predicate verbs have not changed.

The infinitive is a non-predicate verb form with the structure of "to+ verb prototype", in which to is not a preposition, but a symbol of the infinitive, called an auxiliary word, and the infinitive has no change in person and number. The infinitive of the verb and the noun behind it form an infinitive phrase, which can be used as subject, predicative, object, complement, attribute and adverbial in a sentence.

As a theme, for example:

It is difficult to be a doctor. It is difficult to be a doctor.

It is not easy to learn English well. It is not easy to learn English well.

Saying is believing. I'll believe that when I see it.

When the infinitive (phrase) is the subject, in order to avoid top-heavy sentences, we can use "it" as the formal subject and put the real subject-infinitive (phrase) at the back of the sentence. For example, the above sentence can be expressed as:

It is difficult to be a doctor.

It is not easy to learn English well.

Planting trees in spring is very important.

If the action of the infinitive is done by who, a phrase guided by the preposition for can be added before the infinitive, which is called the compound structure of the infinitive. Example:

Reading English aloud in the morning is good for us.

Reading English aloud every morning is very beneficial to us.

It is important for students to use English every day.

It is very important for students to use English every day.

As a predicative: (Formally, the predicative is located after the copula. In a sense, predicative is a grammatical component that answers the subject "What" or "How". )

Verb infinitive (phrase) as predicative is often used after the copula be. Example:

His job is driving a car. His job is driving a car.

My job is to feed animals. My job is to raise animals.

Her ambition is to be a doctor. Her ideal is to be a doctor.

Step 3 become an object

Verb infinitives (phrases) can be used as objects after some verbs. Verbs that can use infinitives as objects are: start, start, want, forget, remember, show, learn, like, hate, love, ask and so on. Example:

I want to tell you a story. I want to tell you a story.

They start work at eight o'clock every morning. They start work at 8 o'clock every morning.

Don' t neglect to lock the door

Would you like to have a picnic with us tomorrow? Would you like to have a picnic with us tomorrow?

* If and connects two infinitives, the second infinitive usually saves "to":

He wants to go swimming with us. He wants to go swimming with us.

(2) If the infinitive (phrase) used as an object is very long, it can be used as a formal object.

I find it interesting to learn English with you. I think it's interesting to learn English with you.

He found it difficult to catch up with others. He found it difficult to catch up with others.

4. As an object complement. For example:

The teacher asked us to read English for half an hour in the morning.

The teacher asked us to read English for half an hour in the morning.

Teachers often tell Jim not to spend too much time playing computer games.

Teachers often tell Jim not to spend too much time playing computer games.

Please let me help you. Let me help you.

The infinitive is used as the complement of the object, indicating the action of the object. Verbs that can use infinitives as object complements are: tell, ask, want, like, invite, take risks, help, etc. However, infinitives used as object complements after sensory auditory verbs such as let, make, see, watch, hear, feel, notice and have generally omit the infinitive symbol "to", which can be summarized into the following three sentence patterns:

1. You can't omit the infinitive of to as the object complement:

Tell/ask/want/want/hope/like/invite/encourage/teach sb. Do sth.

The teacher told us to come early tomorrow.

I want you to go now. I want you to go now.

Her parents want her to be a teacher. Her parents want her to be a teacher.

2. Save the infinitive of "to" as the object complement:

Let/make/own sb. Do sth.

Now let the boy out. Let the boy out.

The boy made the baby cry. The boy made the child cry.

See/see/hear/notice/feel sb. Do sth.

I saw the students playing basketball on the playground yesterday.

I saw the students playing basketball on the playground yesterday.

I often hear girls singing in the next room.

3. What can be saved or not:

Help sb. Do sth.

I often help my mother with housework.

I often help my mother with housework.

The negative form of infinitive is to add not directly before to. Example:

Tell them not to play football in the street. Tell them not to play football in the street.

(2) The negative form of the infinitive that omits to is to add not directly before the verb. Example:

Tell the boy not to go. Tell the boy not to go.

(3) If the active voice is changed to the passive voice, the infinitive used as the object complement becomes the subject complement, and the infinitive does not save "to", that is, the original saved plus sign, for example:

The boy made the baby cry.

The boy made the baby cry. The boy made the child cry.

Verb (abbreviation of verb) infinitive as attribute

The infinitive is often used as an attribute, a modifier noun or indefinite pronouns, and it is a postattribute after the modified word. Example:

Who was the first to arrive? Who arrived first?

She has no paper to write on? She has no paper to write on?

The best way to learn English is to use it. The best way to learn English is to use it.

When is the best time to grow vegetables? When is the best time to grow vegetables?

Do you have anything to drink? Is there anything to drink here?

* When an infinitive (phrase) is used as an attribute to modify a noun, it has a verb-object relationship with the modified word. If the verb in the infinitive is an intransitive verb, a preposition that requires meaning should be added after it. Example:

I have no chair to sit on. I have no chair to sit on.

He has no house to live in. He has no house to live in.

An intransitive verb infinitive as an adverbial of purpose;

The infinitive is often used as an adverbial of purpose after intransitive verbs such as go, come and hurry to express the purpose.

He went to see his sister yesterday. He went to see his sister yesterday.

They got up early in order to catch the early bus. They got up early in order to catch the early bus.

Sometimes you can put the infinitive (phrase) at the beginning of a sentence in advance to emphasize the purpose. Example:

In order to learn English faster and better, he went to England.

In order to learn English faster and better, he went to England.

As an adverbial, infinitive can express the purpose, result, reason, condition and way of action.

A. for meat

When expressing the purpose, the infinitive can be placed at the beginning of the sentence or at the end of the sentence. But in front of a sentence, infinitives are often separated from sentences by commas; However, commas are generally not used at the end of sentences. For example:

In order to get there on time, we set off at five in the morning. In order to get there on time, we set off at five in the morning.

He went there to enjoy the fresh air. He went there to enjoy the fresh air.

Comparison: doing, doing for the sake of doing, so doing can all indicate the purpose, but doing and doing for the sake of doing can be located at the beginning and end of the sentence; And so to do can only be placed at the end of the sentence

He bought some wood and steel yesterday to build a house.

He bought some wood and steel yesterday to build a house.

He bought some wood and steel yesterday to build a house. He bought wood and steel yesterday to build a house.

B. Table results

The infinitive indicates the result of the predicate action in the following structure, and its position is generally at the end of the sentence.

The infinitive of (1) indicates the terminal verbs find find, see, hear, learn, discover, and often indicates unexpected results. The infinitive is often modified by adverbs such as never and only. For example:

I hurried to the railway station yesterday, only to find that the train had left. When I arrived at the railway station yesterday, I found that the train had left.

I went to the classroom and found it empty. I went to the classroom and found it empty.

(2) In "so+ adjective/adverb +as+to do". For example:

The scenery is so beautiful that many people come here every year. The scenery is beautiful and attracts many people here every year.

(3) in "adjective/adverb+pass +to do". For example:

He ran fast enough to catch up with Li Lei. He ran so fast that he caught up with Li Lei.

(4) in "so+ adjective/adverb +a(n)+n.+as+to do". For example:

This is such an interesting story for interesting children. This is a very interesting story, which makes the children very interested.

(5) In "such+adjective/adverb+noun +as+to do". For example:

She is a good girl who has helped you make great progress. She is a very good girl and has helped you make great progress.

(6) In "Tai+Adjective/Adverb+Doing". For example:

They walked too slowly to catch the early bus.

C. Table reasons

When the infinitive expresses the reason, it is usually placed at the end of the sentence, explaining the reason why the subject produces some emotions and emotions (happy, happy, sad, worried, sorry, excited). For example:

I am very happy to hear that Li Lei was elected as the secretary. I'm glad to hear that Li Lei was elected secretary of the Party Committee.

D. Form conditions

When an infinitive expresses a condition, it is usually placed at the beginning of a sentence. For example:

When heated, liquid will turn into gas. If heated, liquid will turn into gas.

E. tabular mode

The infinitive can be followed by if/ as if, for example:

He moved his mouth as if to say something. His lips moved as if to say something.

When infinitives are used with interrogative words, they can be used as the subject, object and predicative of sentences. Example:

The question is where to get a computer.

Nobody knows how to do it. Nobody knows how to do it. (Guest)

I really don't know which to choose. I really don't know which to choose.

When and where to hold the party is still unknown. (theme)

When and where the party will be held is unknown.

When infinitives and interrogative words are used as objects, they can sometimes be changed into object clauses. Example:

I don't know what to do next. I don't know what to do next

I don't know what I should do next.

Sorry, I can't help it