7-3. Грамматические роли инфинитива

Инфинитив может играть роль подлежащего, комплемента и дополнения.
Он может заменять that-clause в следующих примерах:

I hope [that I'll be able to come].
I hope [to be able to come].

We consider [that he is very trustworthy].
We consider [him to be very trustworthy].

We thought it [wrong that he should be punished].
We thought it [wrong to punish him].

(при этом такая замена возможна не со всеми глаголами и только в том случае, если и личный глагол и инфинитив имеют общее подлежащее и относятся к одному и тому же времени)

SUBJECT

1. Инфинитив может играть роль подлежащего:

To hesitate is fatal/a pity.
To practice regularly is important.
To wait for people who were late made him angry.

Но в современном английском обычно в таких случаях употребляется предварительное it:

It is fatal/a pity to hesitate.
It was good/a great pleasure to see you.
It's important to practise regularly.
It made him angry to wait for people who were late.

В начале предложения может лучше звучать герундий:

Selling insurance is a pretty boring job (более естественно, чем To sell insurance ... )

COMPLEMENT

Инфинитив может употребляться в роли комплемента подлежащего:

The main thing is to relax.
Your mistake was to write him that letter.
Your task is to get across the river without being seen.
My ambition was to retire at thirty.

Есть разница между:

Your mistake was not to write that letter. (You failed to write)
Your mistake was not to write a letter but to write so rudely. (You did write: your mistake was to write rudely)

Избежать двусмысленности может так:

Your mistake was not so much to write a letter as to write so rudely.

(1) В таких предложениях может употребляться предварительное it:

It is your task to get across the river without being seen.
It was my ambition to retire at thirty.

(2) После глагола-связки be to-infinitive может обозначать будущее действие или состояние:

The best item on the programme is still to come.
If we are to win this match, we must all do our very best.
It was 1491. Columbus was to reach America a year later.
The Prime Minister is to speak on television this evening
I don't know what is to happen to us.

Такая же конструкция выражает и приказ или запрещение: You are (not) to stand here.
(3) Инфинитив употребляется и с другими глаголами-связками:

He grew (up)/came/got (informal) to be rather selfish.

2. Инфинитив часто употребляется в роли комплементации (т.е. необходимого завершения смысла словосочетания) прилагательного или существительного:

I'm anxious to contact your brother.
You have the right to remain silent.