Functions of Infinitive

Functions of the to-infinitive

Function 1

to-infinitive is used to indicate the purpose/intention of an action 
(so here to-infinitive = ‘in order to’ or ‘so as to’)

He came to collect his payment. (to collect = in order to / so as to)

Function 2

to-infinitive is used to indicate what something will (or can) be used for.
(here to-infinitive will come after a noun or pronoun and modify it)

I would like a glass of milk to drink.

In most such cases, the to-infinitive works as a post-modifier of:

• abstract nouns (e.g. desire, refusal, wish, ability etc.) and
• indefinite pronouns (e.g. something, one, anything)

Have a look at the following examples:

I have no desire to play for your club. (desire - abstract noun)
There is no need to jump. (need - abstract noun)
You have no one to talk to. (one - indefinite pronoun)

Function 3

to-infinitive is used to make a comment/judgement about a noun/noun phrase.

Pattern: Subject + be + noun phrase + to-infinitive

It was a rough strip to land.
That is a dangerous way to drive.
Mayank is the best candidate to hire.

Function 4

to-infinitive is often used after certain adjectives.

Pattern: Subject + be + adjective + (for/of someone) + to-infinitive

She is perfect for you to marry. (perfect - adjective)

Function 5

To express purpose implying future time, we use the following pattern:
Pattern: Verb (first action) + to + $V_1$ (infinitive) (second action)

I am going to the USA to have bought some laptops for my company. (incorrect)
I am going to the USA to buy some laptops for my company. (correct)

To express completion of action, we use the following pattern:
Pattern: Verb (second action) + to have (been) + $V_3$ (Perfect infinitive) (first action)

Mr. Bose is believed to die in a plane crash. (incorrect)
Mr. Bose is believed to have died in a plane crash. (correct)

Functions of the zero infinitive

Function 1

Bare infinitive (infinitive without ‘to’) is used after modals.

I will play today.

You should work smartly.

Function 2

‘Need’ and ‘Dare’ take bare infinitives when they are used as auxiliary verbs in negative and interrogative sentences.

You need not to worry. (incorrect)
You need not worry. (correct)

Need I to take this test? (incorrect)
Need I take this test? (correct)

We dare not to disobey the inspector. (incorrect)
We dare not disobey the inspector. (correct)

Function 3

Bare infinitive is also used after – ‘had better, had sooner, had rather, would rather, would better, would rather, sooner than, rather than’.

You had better ask permission.

I would rather die than be a traitor.

Verbs and Infinitives

Some verbs are almost always followed by to-infinitives and some almost always by bare infinitives.

Let’s see some examples:

Concept 1: Verbs that are followed by bare infinitives

We use bare infinitive after the following verbs – bid, make, help, feel, see, watch, hear (when they are used in Active voice).

My dad made me do the home work. (do - bare infinitive)

I watched her go. (go - bare infinitive)

But when these verbs are used in passive voice, we use ‘to + $V_1$’ (Infinitive) and not bare infinitive after them.

I was made to clean the car. (to clean – to-infinitive)

Concept 2: Let

With let we always use bare infinitive (both active and passive voice)

I will not let her go. (Active voice)
Bad habits must be let go. (Passive voice)

Let me to go there. (incorrect)
Let me go there. (correct)

Concept 3: Want

With ‘want’ we use ‘to-infinitives’ almost always, except some cases.

I want work for you. (incorrect)
I want to work for you. (correct)

Concept 4

We use bare infinitive after verbs of perception (e.g. see, hear, feel etc.)

Pattern: verb + object + bare infinitive.

She saw him fall from the horse.

I heard him fire the gun.

He felt a snake crawl up his leg.

Question words and Infinitives

Concept 1

to-infinitive is often used with question words (how, where, what, who, and when).

This question word + to-infinitive pattern often comes after verbs such as ask, decide, explain, forget, know, show, tell, understand, learn, teach, discover etc.

He asked me how to use the Camtasia video-editor.
I have no idea where to place this puzzle piece.
Can you tell what to do?
Let me know when to press the alarm button.
I’m not sure I know who to call.

They know to write letters. (incorrect)
They know how to write letters. (correct)

Concept 2

After ‘why’ the bare infinitive is used (used for making suggestions).

Pattern: Why + (not) + Bare infinitive …….? (Interrogative sentence)

Why tell anyone? (tell - bare infinitive)

Why to learn English if it is difficult to learn. (incorrect)
Why learn English if it is difficult to learn. (correct)

Why not to go to the temple every day? (incorrect)
Why not go to the temple every day? (correct)

Extra Books and Tools

If you prefer to learn via books, or want some good English Grammar books for reference purposes, you may read this article which enlists some of the books recommended by us.