The infinitive can be used in different syntactic functions.
Subject:
To make mistakes is easy. To defrost this fridge takes ages.
The infinitive as a subject may precede the predicate. In Modern English, this is unusual in informal style. The infinitive more often follows the predicate, and the sentence opens with the introductory it, which is “a formal subject”.
It’s easy to make mistakes.
Predicative:
Your task is to get across the river without being seen.
Part of a predicative:
He’s easy to amuse. She is nice to talk to.
Part of a compound verbal predicate:
She seems to be crying.
- modal predicate
The cleaning is to be finished by midday.
- aspect predicate
Before daylight it started to drizzle.
Object:
Many verbs can be followed by an infinitive as an object, for example:
afford consent learn prefer swear
agree decide like prepare trouble
arrange except love pretend try
ask fail manage promise want
attempt forget mean propose wish
beg hate neglect refuse wait
care help offer regret
choose hesitate omit remember
claim hope plan threaten
I don’t want to see you again.
Some of these verbs can be followed by the Objective with the Infinitive Construction or the For-to-Infinitive Construction (see next function).
I want her to be happy.
An infinitive can be used after the questions words who, what, where, etc. (but not usually why).
I wonder who to invite. (=…who I should invite).
An infinitive is used as an object after adjectives such as pleased, lucky, sorry, afraid, etc.
You were very lucky not to be killed.
Part of a Complex Object (as the verbal element in the Objective with the Infinitive Construction and the For-to-Infinitive Construction, see …):
Why won’t you let me explain?
Attribute:
An infinitive modifies abstract and class nouns, indefinite and negative pronouns, ordinal numerals, the adjectives next and last.
I told her about my decision to leave.
The infinitive can express the idea of obligation, possibility, purpose, an intended effect.
Have you got a key to open this dor
Adverbial modifier:
a) an adverbial modifier of purpose
I sat down to rest.
In order and so as are normal before stative verbs like be, have, know and before negative infinitives.
I watched him in order to know more about him.
b) an adverbial modifier of result
In this function infinitive is chiefly used after adjectives modified by enough or too.
Mr. Evans was too busy to see anyone.
An infinitive can be used after a noun modified by enough, too much/little, etc.
There was enough light to see what I was doing.
It is also found after so – Adjective – as or such – a Noun – as. The result is negative.
He was so weak as to be unable to work.
c) an adverbial modifier of comparison
An infinitive is introduced by the conjunction as if or as though.
She moved her hand towards his lips as if to stop him.
d) an adverbial modifier of attendant circumstances
I arrived home to find that the house had been burgled. (=…arrived and found that…)
e) an adverbial modifier of cause
The infinitive of see and hear can explain the cause of a (false) impression. It is usually followed by you’d think or a similar expression.
To hear her talk, you’d think she was made of money.
f) parenthesis
To speak the truth, I was a little troubled.
6.1.
