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I have already written about this impersonal form of the verb in English. The article is called " ". I recommend reading it first, as it helps you get a general idea of ​​the infinitive. Remember that the infinitive is the indefinite form of the verb. The standard form of the infinitive in English is formed using the base (dictionary) preceded by a particle to. But there are a certain number of cases where it is used without this particle. Here we are already talking about such a thing as "naked infinitive" - bare infinitive. To articulate when we need particle infinitive to , and when without it, I am writing this article.

But before we go directly to listing these cases, I would like to repeat what forms the English infinitive can have (using the example of the verb to leave- leave, leave

1. Present Active– (to) leave
   

   I'm ready to see him now. - I'm ready to see him now (real)

   George wants to find a new job next month. George wants to find a new job next month (future)

2. present passive– (to) be left
   

   She expects to be presented a special gift on the anniversary. She is waiting for a special present for her anniversary.

   He hopes to be invited to his daughter's wedding. He hopes to be invited to his daughter's wedding.

3. Present Continuous Active– (to) be leaving
   

   My mother seems to be painting the walls. It seems my mother paints the walls.

   They seem to be building a house. It looks like they are building a house.

4. Perfect Active– (to) have left
   

   He claims to have infected with flu about 10 people. He claims that he has infected about ten people with the flu.

   I seem to have made a short film. “I think I made a little film.

5. Perfect Passive– (to) have been left
   

   A famous journalist said to have been killed in Egypt. - They say that a well-known journalist was killed in Egypt.

   The unique painting is said to have been sold for $20 millions. - They say that a famous painting was sold for 20 million dollars.

6. Perfect Continuous– (to) have been leaving
   

   courtney claims to have been working for this company for 3 years. Courtney states that she has been working for this company for three years.

   They are known to have been developing a new medicine for several years. It is known that they have been developing a new drug for several years.

infinitive with particle to

So, we move on to the main topic of this article. I would like to list the cases when it is necessary to use the standard form of the particle infinitive to. This particle will come before the infinitive if:

1. We express any purpose defined by the infinitive verb.
   

   She returned home to ask for some extra money. She returned home to ask for more money.

   We are leaving in ten minutes to catch the train to London. We are leaving in 10 minutes to catch the train to London.

2. The infinitive will follow these verbs: advise, agree, appear, decide, expect, hope, manage, offer, promise, refuse, seem, want, allow, pretend and etc.
   

   He offered me to stay at home instead of going out. Instead of going somewhere, he suggested that I stay at home.

   Why did you refuse to conduct these negotiations? Why did you refuse to negotiate?

3. The infinitive is preceded by the combination "certain verb +". A list of words acts as certain verbs: know, decide, ask, learn, remember and etc.
   

   She wants to know why you decided to spend your vacation abroad. She wants to know why you decided to spend your holiday abroad.

   I explained how to use the new washing machine. I explained how to use the new washing machine.

   By the way, if a sentence has two infinitives with a particle to, which are connected by English unions and, or, particle to before the second can be omitted.

   I didn't decide where to go and stay. I haven't decided where to go and where to stay.

   My boss explained how to write an article and take photos. My boss explained how to write an article and take photos.

4. The infinitive is used after such as happy, nice, happy, sorry, willing, afraid, ashamed and etc.
   

   I am willing to overlook your mistakes, but I can't do this. “I want to ignore your mistakes, but I can’t do it.

   It is nice to see you again. - Nice to see you again.

5. It is preceded by:
   

   My friend is too shy to take the initiative in acquainting with people. My friend is too shy to take the initiative when meeting people.

   I've got enough money to buy a flat downtown. I have enough money to buy an apartment in the city center.

6. We make a proposal based on the construction " it+be+ adjective "(+ of+ or ).
   

   It was nice of him to tell the truth about his past. It's very good that he told the truth about his past.

   It's important to receive all necessary books before we start our lessons. It is important that all the necessary books arrive before we start studying.

7. It is accompanied by the expression would like / would love / would prefer. Each of them implies that someone would like to do something.
   

   I would like to move to London. - I would like to move to London.

   I would prefer to go by car. – I would prefer to go by car.

8. The sentence contains the word only, which helps to express dissatisfaction with some result or event.
   

   She went to work only to meet her angry boss. She went to work only to meet an angry boss.

   I rushed to the railway station only to make sure that the train had already left. I rushed to the station just to make sure the train had already left.

9. We use it after such nouns and pronouns as something, somewhere, anyone, nothing. Usually in this way we show that something is necessary or possible.
   

   Let's give them something to talk about. Let's give them a topic to talk about.

   take something to eat on our trip. Take some food for the journey.

10. The sentence contains a combination be+the first / the second, etc. / next / last / best and etc.
    

    You were the first to congratulations me with my birthday. You were the first to wish me happy birthday.

    I am the next to choose where to go on holidays. Next I choose where to go on vacation.

Infinitive without particle to

Cases in which we use infinitive without particle to , i.e bare infinitive, far less. But you need to know them. After all, you do not want to make grammatical errors in this topic? So we use the bare infinitive after:

1. ( , , , , etc). The exception is modal verbs. / / / , which are used with the infinitive with to.
   

   We should tell our parents about the party. We should tell our parents about the party.

   He must apologize for his words. He should apologize for his words.

   She ought to be more polite to other people. She should be more polite to people.

2. After verbs let, make, see, hear, feel.
   

   We saw them kiss. We saw them kissing.

   I won't let her marry without my blessing. “I will not let her marry without my blessing.

   But, if these verbs are used in, they are accompanied by an infinitive with a particle to.

   He was heard to say either he was trying to kill someone or someone was trying to kill him. “He was heard to say that either he was trying to kill someone, or someone was trying to kill him.

3. After expressions / would rather.
   

   You'd better sit down. - You'd better sit down.

   I'd rather go to jail than serve in the military. “I'd rather go to jail than serve in the armed forces.

4. In interrogative sentences that begin with the words why not? (why not).
   

   Why not go to the cinema? Why not go to the cinema?

At first it may seem that there is no end to the information here! But actually it is not. When studying English, you somehow come across the mentioned verbs, phrases, constructions, and remember which infinitive goes with them in a complex. Here is just a list of situations that may come your way. Don't get lost!

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Test

The use of the infinitive with the particle to and without the particle to

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Some verbs are used with both an infinitive and a gerund after them. Sometimes it makes sense, sometimes it doesn't. Below are examples of both cases.

Let's start with these three verbs. Depending on what is behind it - a gerund or an infinitive, the meaning of the expression changes

Forget
Remember
Regret

All of them relate to memory, so to speak (for some reason I noticed this). Gerunds after them are used to show that something was done before the moment of speaking.

For example:

I remember giving him a gift - I remember that I gave him a gift

You forget meeting me in Italy - you forgot how you met me in Italy

I so regret moving to Moscow - I'm so sorry that I went to Moscow

In each of these three examples, the action happened before the moment of speaking.

If these verbs are used with the infinitive, then the conversation will go about something that has not happened yet.

For example:

Don't forget to call me back - don't forget to call me back

Make sure you remember to buy a new phone - do not forget to buy a phone

I regret to tell you that you're not my girlfriend anymore - I'm sorry, but you're not my girlfriend anymore

Let's now compare almost identical sentences, but used in one case with the infinitive, in the other with the gerund.

John remembers buying a new phone at the supermarket - John bought a phone and remembers this (this is an action, this moment)

John remembers to buy a new phone at the supermarket - John remembers to buy a phone when he is in the supermarket

Emily forgot calling me back - Emily forgot that she called me back

Emily forgot to call me back - Emily forgot to call me back

I regret telling you that you are not my girlfriend anymore - I'm sorry that I told you that you are no longer my girlfriend (I mean, I'm sorry I had to do / say and upset you)

I regret to tell you that you are not my girlfriend anymore - I'm sorry, but I must say that you are no longer my girlfriend

Stop
Go on

These two verbs denote actions that began at the moment of speaking. If they are used with a gerund, it means an action that has continued (go on) or finally stopped (stop)

For example:

I stopped drinking alcohol - I no longer drink

I went on drinking alcohol - I started drinking alcohol again (from a certain point)

If these two verbs are used with an infinitive, it means that the action has begun right now or will begin in the future

I stopped to call my mother - I stopped doing something to call my mother

Douglas went on to become a boss - Douglas eventually became the boss

And now let's, again, compare these verbs used with the infinitive and gerund

I stopped playing the guitar at seven - I played the guitar, but stopped playing it at seven o'clock

I stopped to play the guitar at seven - I did something, but stopped doing it at seven o'clock and started playing the guitar

Olivia went on speaking about her problems - Olivia continued to talk about her problems

Olivia went on to speak about her problems - Olivia, later in the conversation, continued to talk about her problems

like doing = in general

like to do = like to do something when there is a certain choice

He likes playing football in the morning. – He likes to play football in the morning (he just loves this time, it's not about the fact that he has a choice)

He likes to play football in the morning - When there is an opportunity to play football, he prefers to do it in the morning

prefer to do = if there is a choice, then I will choose

prefer doing = simply preferring one over the other

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In English infinitive(Infinitive) - this is, which denotes an action, but does not indicate a person and a number. In Russian, the English infinitive corresponds to the indefinite form of the verb, which answers the questions “what to do? what to do?": to live - to live.

The formal sign of the infinitive is the particle to:

to write- write, to read- to read, to drink- drink, to think- think.

If the verb is preceded by a particle to, then in front of you is the infinitive (or the indefinite form of the verb). Sometimes the infinitive can be used without a particle to.

The negative form is formed by a particle not, which is placed before the infinitive: not to use - do not use.

It is difficult to use .- Hard use.
It is difficult not to use .- Hard do not use.

Infinitive forms

In English, the infinitive has 6 forms (unlike Russian, which has only one form). To understand well the meanings of the forms of the infinitive, it is necessary to have an idea of ​​\u200b\u200band the verb.

Simple infinitive. Indefinite Infinitive

infinitive in the form Indefinite (Simple) or simple infinitive is the basic form and represents the verb in the dictionary (for convenience, in the dictionary the particle to often omitted). This form of the infinitive belongs to the same tense as the verb that precedes it.

I was glad to see her. — I was glad to see her (simple active infinitive).
The child didn't like to be washed. - The child did not like being washed (a simple infinitive in the passive voice).

Compare the use of the simple infinitive in active and passive voice: to help - to be helped
I am happy to help you. - I am glad to help. (I'm glad I'm helping).
I am happy to be helped. - I'm glad they're helping me.

Perfect infinitive. Perfect Infinitive

infinitive in the form Perfect or perfect infinitive denotes an action that precedes the action of the verb-predicate.

I was very happy to have met you. — I am very glad that I met you (active perfect infinitive).
Sorry not to have noticed you. — I'm sorry I didn't notice you (active perfect infinitive).
The child was happy to have been brought to the circle. The child was happy to be taken to the circus (passive perfect infinitive).

Compare the use of a simple (Simple Infinitive) and a perfect (Perfect Infinitive) infinitive in the active voice: to see - to have seen
I am happy to see you. - Glad to see you. (Glad to see you.)
I am happy to have seen you. - I'm glad I saw you.

Long infinitive. Continuous Infinitive

infinitive in the form continuous or long infinitive emphasizes the duration of the action that occurs simultaneously with the action of the verb-predicate. This form is used only in the active voice.

He seems to be writing something. - He seems to be writing something now (long infinitive in the active voice).

Perfectly continuous infinitive. Perfect Continuous Infinitive

infinitive in the form Perfect Continuous or perfect continuous infinitive emphasizes that the action began earlier than the action of the verb-predicate, lasted for some period of time and is still going on. This form is also not used in the passive voice.

He seemed to have been writing all day. He seemed to have been writing all day.

Forms of the infinitive in the table

The meaning of different forms of the infinitive in the table
Infinitive forms	What am I happy about?
Simple	I am happy to speak to you.	Glad to talk to you. (I always rejoice when I talk to you).
continuous	I am happy to be speaking to you.	I'm glad I'm talking to you now.
Perfect	I am happy to have spoken to you.	I'm glad I talked to you.
Perfect Continuous	I am happy to have been speaking to you.	I am glad that I have been talking to you for a long time (all this time).
simple passive	I am (always) glad to be told the news.	I'm always glad when they tell me the news.
Perfect Passive	I am happy to have been told the news.	I'm glad I got the news.

The use of the infinitive without the particle to

Most often, the infinitive in English is used with the particle to, but there are cases when the particle to not used before the infinitive.

The infinitive is used without particle to in the following cases:

• After can, could, must, may, might, will, shall, should, would And need (in the value of modal). Exceptions are modal verbs have to, ought to, be to.

• IN complex addition after verbs of sense perception feel(feel), hear(hear), see(see), watch(observe), notice(notice):
  

  I saw him leave the office. — I saw him leave the office.
  I heard him go down the stairs. — I heard him come down the stairs.
  

  But: if the listed verbs feel, see, hear, watch, notice are used in the passive voice, then the infinitive is preceded by a particle to:
  

  He was seen to leave the office. We saw him leave the office.
  

• In complex addition after verbs make(meaning "force, compel") And let(meaning "permit, allow"). Again, if these verbs are in the passive voice, then the infinitive is used with the particle to.
  

  I can't make you take this medicine. “I can't force you to take this medicine.
  We let her go to the party. We let her go to the party.
  She was made to rewrite the test. - She was forced to rewrite the test (was made is a passive verb).
  

• After the verb help(to help) the infinitive can also be used with the particle to, and without it. Both options are acceptable, while the option without to less formal.

Infinitive [?n?f?n?t?v] Infinitive

Infinitive in English - a form of a verb that expresses an action without indicating person, number and mood, and performs the functions of a verb or noun. The infinitive answers the questions: "What to do?", "What to do?". Negation is formed by adding the particle not before the infinitive. The infinitive can be used either with or without the particle to.

In English, the infinitive has six forms (four of them are active, and two are passive).
1. Infinitive in active voice:
but. Simple Infinitive
b. Continuous Infinitive
in. Perfect Infinitive
d. Perfect Continuous Infinitive
2. Passive infinitive:
but. Simple Infinitive Passive
b. Perfect Infinitive Passive

Infinitive form	Pledge
	Valid	Passive
Simple	to + I	to be + III
	to paint	to be painted
continuous	to be + IV	---
	to be painting	---
Perfect	to have + III	to have been + III
	to have painted	to have been painted
Perfect Continuous	to have been + IV	---
	to have been painting	---

The infinitive is used in three syntactic structures:
1. Object infinitive turnover (alternative name: "Complex object")
In this structure, the infinitive is used in most cases. The object infinitive phrase looks like this:
Noun/Personal Object Pronoun (me, you (singular), him, her, it, us, you (plural), them) + Infinitive
In a sentence:
Subject + Predicate + Object infinitive + Secondary members
She wants him to call her. She wants him to call her.
2. Subjective infinitive (alternative name: "Compound subject")
Noun/Personal pronoun in the common case + Personal verb as a predicate (more often in the passive voice) + Infinitive
In a sentence:
Subject + Subjective infinitive + Secondary members
Hannah seems to know him. Hannah seems to know him.
3. Infinitive turnover with the preposition for
For + Noun / Pronoun + Infinitive
In a sentence, this turnover can be in different positions, depending on what role it plays.
but. The role of the subject
For him to meet with new people is easy. He easily meets new people.
b. The role of the add-on
She waited for the bus to come. She was waiting for the bus to come.

Using the Simple Infinitive
1. The action indicated by the infinitive and the action expressed by the personal verb or adjective to which the infinitive refers occur simultaneously.
Note: After modal verbs and their equivalents, the action expressed by the infinitive may refer to the future tense.
Michelle was glad to discuss the next meeting with Daniel. Michelle was happy to discuss her next meeting with Daniel.
It may be stuffily in the hall. The room can be stuffy.

2. After such verbs as:
to desire
to expect
to hesitate not to decide; hesitate
to intend
to mean
to try
to want
to manage
to decide
to fail
to begin
to continue
to arrange
to agree
to prefer
to seem
to ask
to promise
to forget
to demand
to remember
to hate
to like
to hope
to love
and etc.
and also after the expressions:
in order to
so as to
It is astoundingly to remember such long-ago events. It's amazing to remember such a long time ago.
Ian went back home in order to close the windows. Ian returned home to close the windows.
3. After nouns corresponding to verbs.
to decide - decision
to refuse - refusal to refuse - refusal
to propose - proposal to offer - offer
to wish - wish to wish - desire
and etc.
His decision to refuse such an offer is foolishly. His decision to refuse such an offer is stupid.
4. After adjectives expressing attitude, encouragement, disapproval, etc.
It was kind of you to accompany me on a journey to New Zealand. It's nice of you to accompany me on this trip to New Zealand.
Michael was pleased to visit some places of his childhood. Michael was pleased to visit the places of his childhood.

Using Continuous Infinitive
To indicate a long action that occurs simultaneously with the action, expressed by verbs in the personal form or by the adjective to which the infinitive refers. Also, a long infinitive can be used after modal verbs.
The weather seems to be improving. The weather seems to be getting better.

Using Perfect Infinitive and Perfect Infinitive Passive
1. To denote an action that occurred before another action expressed by a personal verb or an adjective to which the infinitive refers. Very often Perfect Infinitive and Perfect Infinitive Passive are used with verbs:
to acknowledge
to appear
to believe
to consider, consider
to find
to happen
to know
to pretend
to report
to say
to seem
to suppose
to think
to understand
Noah was sorry to have missed the meeting. Noah regretted missing the meeting.
2. To denote an action that will be completed by a certain point in time in the future.
She hopes to have left work until nine o "clock in the evening. She hopes to leave work before nine o'clock in the evening.
3. To express the assumption that the action has already happened, after the modal verbs may, might, could.
Carter may/might/could have fulfilled everything without us. Maybe Carter did it all without us.
4. After the modal verb must to indicate a logical judgment.
Christian must have been here: there are strange footprints on the floor. Christian must have been here: there are footprints on the floor.
5. In negative and interrogative sentences with the verb can to express doubt or surprise.
Can she have gone away without notice? Did she leave without warning?
6. After the modal verbs should, would, could, might, ought to to express an action that could have happened, but did not.
He should have ended this talk. He had to end this conversation.
7. To refer to an action that was performed despite the fact that it was undesirable.
He needn "t have bought the car on credit. He shouldn't have bought a car on credit.
8. To indicate the likelihood of what happened, after the modal verbs can and could in the negative form: can "t and couldn" t, respectively.
You couldn't have run five kilometer for ten minutes. It can't be that you ran five kilometers in ten minutes.
9. To denote an action that did not happen despite hope, desire or expectation, after verbs:
to expect
to intend
to hope
to mean
and after the expression would like (would like)
I intended to have warned him, but I forgot. I meant to warn him, but I forgot.

Using the Perfect Continuous Infinitive
To indicate a long action that began before the action expressed by the personal verb or adjective to which the infinitive refers.
Leah is known to have been working in this firm for six years. It is known that Lea has been working in this firm for six years.

The use of the infinitive without the particle to
1. After auxiliary and modal verbs, except for ought (to), to have (to), to be (to).
He must come back immediately. He must return immediately.
Brandon is to come at six o "clock in the morning. Brandon should come at six o'clock in the morning.
2. After verbs perception in the active voice.
Andrew saw her looking out of the window. Andrew saw her looking out the window.
(Other verbs of feeling and perception are in the material "".)
3. After the verbs to let, to make, to have all three in the meaning of "get", and also to know in the meaning of "to know" in the active voice.
Don "t let him abuse you. Don't let him abuse you.
4. After expressions:
had better
would rather
cannot but
nothing but nothing but
I would rather buy a sport bike. I'd rather buy a sports bike.
5. In interrogative sentences that begin with the words why not (why not).
Why not go walking? Why don't we take a walk?
6. After the verb help (to help), the infinitive can be used with and without the particle to. But in the passive voice and in negative sentences, the particle to is always used after help.
James will help you (to) carry the traveling bag. James will help her carry her travel bag.
She was helped to carry the travel bag. They helped her carry her travel bag.
7. The particle to is usually not used before the second infinitive when they are connected using conjunctions:
and and
except
but
or
than
What would you choose: to buy a good car or visit Switzerland? What would you choose: buy a nice car or go to Switzerland?
8. The particle to is not used if it is clear from the context what is being said.
Note: If the verb to be is used (to be), then the particle to cannot be omitted.
- Let's play a game of poker! Let's play a game of poker!
- I don "t want (to). I don't want to.
9. After the verb to like, the infinitive phrase is omitted along with the particle to.
Caleb can buy everything he likes. Caleb can buy whatever he wants.
10. If the infinitive turnover plays the role of a subject or attribute and has its own subject, then the preposition for is used before the subject of the infinitive turnover.
He bought a gas sprayer for her to be on the defensive. He bought her a gas canister so she could defend herself.

Infinitive in English is an impersonal form. Like the verb, the infinitive names the action, but unlike the verb, it does not indicate the person and number. In its basic form (Simple Infinitive), the infinitive answers the questions: what to do? what to do?

to purchase - purchase.

The infinitive is also called the "indefinite form of the verb" or "the initial form of the verb."

Table: forms of the infinitive in English (briefly)

The infinitive can have 4 forms in the active voice and 2 in the passive voice.

However, the most common and relevant for study is the form “simple infinitive in active voice” (to ask). In fact, when they say “infinitive”, usually, in most cases, I mean exactly this form - most of this article is devoted to it.

Below we will look at the same table again and analyze each form in detail, but first we need to clarify two more points:

• The infinitive comes with and without the particle to.
• How is the negative form of the infinitive formed?

After that, we will return to the analysis of each form.

Infinitive with to and without to

The infinitive can be used with or without to:

• I want to help you. - I want to help you.
• I must help you. - I have to help you.

Most often, the infinitive is used with to, however, there are a number of cases when the infinitive is used without the to particle, they apply to all forms of the infinitive(i.e. all forms from the table above). I note that most often the infinitive without to occurs after modal verbs, other cases are quite rare.

1. After modal verbs (most common)

Negative form of the infinitive

The negative form is formed by a particle not- it is placed before the infinitive. If the infinitive is with the particle to, the negation of not is placed before it.

I decided not to go to London. I have decided not to go to London.

He asked me not to be late. He asked me not to be late.

I might not come. - I may not come.

All forms of the infinitive in English (detailed)

Let's look at all the forms of the infinitive again:

There are six forms in the table:

1. Simple Infinitive:

I want to ask you - I want to ask you.

2. Simple Infinitive Passive:

I want to be asked- I want to be asked.

3.Continuous Infinitive:

I happened to be asking her about you when you came in. “It so happened that I asked her about you when you came.

4. Perfect Infinitive:

You could have asked me first - You could ask me first.

5. Perfect Infinitive Passive:

She could have been asked by anybody - Anyone could ask her.

6. Perfect Continuous Infinitive:

He seems to have been asking wrong people - Looks like he was asking questions to the wrong people.

Please note that the most common, necessary and important form for studying is Simple Infinitive. In second place - Simple Infinitive Passive. Other forms are used less frequently.

Forms Perfect And Perfect Continuous(i.e. those where there are have) – largely overlap with the topics “ and . If you already know these topics, you will see familiar things, but just from a different angle - everything is explained in more detail below.

Simple Infinitive - simple infinitive (the most necessary form)

The most common and important form of the infinitive for learning is the simple infinitive in the active voice (Infinitive Indefinite Active or Simple Infinitive Active). It is used to refer to an action that:

1. Occurs simultaneously with the action of the main verb:

tell him to stop. - Tell him to stop.

2. Refers to the future tense:

I want you to come with me tomorrow. - I want you to come with me tomorrow.

3. Regardless of the time of commission:

To know such tricks are useful. – Knowing such tricks is useful.

Let's name the main cases of its use.

1. With verbs that do not give the full meaning

The infinitive is often used in combination with verbs that do not make the full sense without it, for example:

• tell- to say / order something,
• Begin- start,
• Continue- continue,
• want- to want,
• Intend- to intend
• try- try, try
• Hope- to hope
• Promise- to promise
• Decide- to decide, to make a decision.

I want to see your permission. - I want to see your permission.

Do you promise to quit smoking? Do you promise to quit smoking?

Nina decided not to sing the agreement. Nina decided not to sign the agreement.

I'll try to help you. - I'll try to help you.

These verbs include modal verbs. I remind you that after them the infinitive is used without the to particle:

I must see your permission. - I need to see your permission.

Can you quit smoking? - Can you quit smoking?

2. To indicate the purpose of the action

In Russian, when it is necessary to express the purpose of an action, we say “to” or “with a purpose”. In English we use the infinitive:

she came to collect her letter. She came (to) pick up her letter.

We came to help you. We have come (to) help you.

I am calling to ask you about dad. - I'm calling you (to) ask about dad.

You sister has gone to finish her homework. Your sister left to finish her homework (left to finish).

In this case to can be replaced by union in order to(with a purpose), the meaning will be the same, but sentences with in order to sound more formal.

You sister has gone in order to finish her homework. Your sister left to complete her homework.

3. Infinitive as subject

As a subject, the infinitive is used in formal speech, more often written.

to be or not to be, that is the question. To be or not to be, that is the question.

To know her is to love her. To know her is to love her.

To visit the Grand Canyon is my life-long dream. “Visiting the Grand Canyon has been my lifelong dream.

to understand statistics, that is our aim. “Understanding statistics is our goal.

4. To indicate the purpose of the subject

If I had known you were coming I would have baked a cake. If I had known that you were coming, I would have baked a pie.

You could have helped him. You could have helped him (but you didn't).

In the case of the verb should there is a hint of regret or reproach:

What should have taken more gas. - We should have taken more gasoline (but, unfortunately, we did not take it).

You should have been prepared for anything! You should have been ready for anything! (but you weren't and that's why you let us down)

Perfect Continuous Infinitive - an infinitive denoting a long-perfect action

Scheme: to have been + Present Participle. Example: to have been talking.

This form is used in the following cases:

1. Long completed action

The infinitive denotes a long action that was performed, but ended before the action expressed by the verb.

The woman seemed to have been crying. The woman looked like she was crying.

He pretended to have been working all day. He pretended to work all day.

2. After modal verbs must, may, should

An assumption is expressed that a certain long-term action took place, but has already ended.

You must have been waiting hours! You must have been waiting for hours!

They might have been talking before you came in. They must have been talking before you came in.

In the case of a modal verb should there is a hint of regret or reproach that some long-term action could occur, but in reality did not occur.

You should have been studying for your test. You should have studied for the test (but you didn't).

Note:

Please note that in all Perfect forms of the infinitive, that is, in forms where there is have, the word itself have never takes shape has, as is the case with the verb in the personal form. Word have in this case, it is part of the infinitive, therefore it cannot be related to a person and a number, therefore it cannot take a personal form has(has = 3rd person, singular).

He has fox. - He has a fox.

The has form is used, because it is a personal form (3rd person, singular) of the verb.

He might have fox. He may have a fox.

Here have- infinitive, it has no person and number.

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