The infinitive: the essentials

Why is it called the infinitive?

The infinitive in English is known as non-finite. That means that you can't tell by looking at it whether it refers to me, you, lots of people, the past, the present or the future. Compare, for example, the verbs in
    He wants to make a cake.
The verb wants has an -s ending here and that tells us that it refers to a singular person, it refers to the third person (it can't refer to me or you) and it is present tense. If we change the form of this verb, we change its function:
    He wanted to make a cake
    They want to make a cake
etc.
The verb make does not tell us any of these things. It will not change if I replace he with you or wants with wanted or want.

Why is it important?

English uses the infinitive in lots of different ways and the important ones are considered here.
Many languages operate differently and some, such as Greek, do not have an infinitive at all. Learners have some difficulty with the infinitive and we get errors such as:

*I went for shopping.
*I want go.
*I can to do it.
*I ought arrive early.

etc.

Two sorts of the infinitive

the bare infinitive: this form of the infinitive is sometimes called the zero infinitive and occurs in these examples:
    What he did was make a terrible mess.
    I can see it.
    I saw him do it.
the to-infinitive: this occurs more frequently. For example:
    I want to go home.
    She tried to help.
    To go to America has been his dream.
    I need a hammer to break it open.
    It is vital to understand the form.
    I had too much work to do.
    Can you tell me how to get to the meeting?

The bare infinitive

after modal auxiliary verbs

The bare infinitive is the most common verb form after modal auxiliary verbs in English. There is a guide to modal auxiliary verbs on this site, linked in the list of related guides at the end.
The modal auxiliary verbs followed by the bare infinitive with examples are:

can
could
had better
may
might
must
shall
should
will
would

You can help
She couldn't help
I had better go
We may arrive late
John might be there
I must confess
We shall not do it
I should think so
They will come
I would enjoy that

Learners have a good deal of trouble with modal auxiliary verbs in English, not least because many of them perform more than one function. One central problem is that they have slightly peculiar structures so we get errors such as:

*I don't can come
*I should to help
*I must to see it

etc.
The most important issue here is that these auxiliary modal auxiliary verbs cannot be followed by the to-infinitive. Learners need lots of practice to get it right.

after verbs of perception

Here are some examples of what's meant here:

I heard it break.
I saw him arrive.
I felt it tremble.
I watched him work.
I listened to her play.
I sensed it vibrate.

We can, of course, also use another non-finite verb with these examples such as
I saw him arriving
I listened to her playing
etc.
However, the sense changes slightly to emphasise that an action was in progress rather than completed.

Learners will frequently be tempted to use the wrong form with these verbs and produce, e.g.,
*I saw him arrived
*I heard it to break
etc.

with make and let

For example,

I made him understand.
I let him leave early.
I didn't make him do the work.
I can't let him go yet.

The difficulty for learners with these two verbs is that other verbs which mean pretty much the same thing take the infinitive with to.
For example:
    I obliged him to come
    I forced him to tell me
    I allowed him to go
    We were permitted to go in
The result, naturally, is that learners will often produce things like:
    *I made him to come
    *She let him to see
etc.

after why

The question word why is very often followed by the bare infinitive.

Why not go to the cinema?
Why tell her no?
Why behave so rudely?

Usually, of course, why is followed by question forms such as in
    Why do you need it?
    Why is the door open?
etc. It can also frequently be used with negative questions as in:
    Why don't we see it?
    Why can't you come?
etc.
Understandably, this causes problems and learners may produce, e.g.:
    *Why not to go?
    *Why shouldn't he to come?
    *Why you go now?
etc. because these sorts of constructions may be the way their languages do things.

The to-infinitive

verbs of expectation, purpose and volition

Some verbs, especially those which refer in some way to the future rather than to past experience, are followed by the to-infinitive. Here are some examples:

I expect to arrive around 6.
I hope to see you.
I've decided to go.
I would love to come.
I want to see you.
I agreed to go.
I intend to do it soon.
I resolved never to talk to her.
I offered to help.
He reminded me to post it.
I went to get the money.
I came to help.
I have nothing to wear.
I want a garden to sit in.

On the other hand, verbs which are based on our experience or refer to past events and situations more commonly take an -ing form verb (also called a gerund in this case):
    I dislike standing in queues
    I remembered meeting her
    She loves reading
    John admitted breaking it
etc.
Understandably, and predictably, this is not an easy area for learners (not least because some teachers assume the forms are random) so we get errors such as
    *I want having it
    *I remembered to meet him the week before
    *She agreed going
    *She agreed go
    *I expect arriving etc.
There's a guide to this area on this site, linked in the list at the end.

The idea of purpose is sometimes treated separately, even being given its own title of 'the infinitive of purpose', but it falls into this category.
It is less simple to see that to is sometimes just an abbreviation of in order to. This confuses. Compare for example:

I agreed to go to the restaurant (to-infinitive used to refer to a future event).
I agreed (in order) to get a bit of peace. (expressing the purpose for the agreement).

If there is a possibility of ambiguity, most speakers will use the in order to formulation.

tell

The verb tell is followed by the to-infinitive:
    I told her to wait
    She told me to leave
    Please tell them to hurry.
Compare make above.
The issue with the verb tell is that it carries three meanings:

It has the meaning of impart information as in, e.g.:
I told him all about the journey
She told me her name
In this sense, the verb is not usually followed by an infinitive but is often followed by a phrase or a noun acting as the object of the verb tell.
In this case, too, the verb takes two objects.
It has an associated meaning of explain as in, e.g.:
I told him why I was late
She told me how to get to the station
etc.
In this sense, the word follows the pattern of other verbs + question words (see below).
It carries the meaning of order / command as in, e.g.:
She told him to wait
They told me to stop
etc.
In this sense only, the verb is followed by an infinitive with to. The infinitive is the structure of choice because the telling precedes the action and so the clause looks forward in time (the telling comes before the action).

after adjectives

Many adjectives are routinely followed by the to-infinitive. Frequently, these take the form of using a dummy subject (it) to stand for the action or event. The adjectives are also very often those which express an opinion about something.

It's important to remember that.
It's interesting to read that.
It was wrong of you to do it so carelessly.
It's good to talk.
She thought she was stupid to go out in the rain.
They said I was dumb to ask too many questions.
It's surprising to see him come early.
It's horrible to talk about.

Just as we can use most adjectives before or following the noun as in, for example:

It's an interesting book. vs. The book is interesting.
The house over the road was ugly. vs. The ugly house was over the road.

etc.

it is also possible, but rarer and usually a little formal, to make the to-infinitive the subject of the sentence as in, e.g.,

To tell him was silly.
To run around looking is useless.
To do it or not is the question.

etc.

As you might expect, learners make errors.

*It's better remembering that.
*It's wrong do it.
*He's silly do that.

after some modal auxiliary verbs

There's a bit of an argument about whether we should analyse a structure like
I ought to write to my mother
as containing ought plus the to-infinitive or ought to plus the bare infinitive. Whichever way it is analysed, the following modal and semi-modal auxiliary verbs come with to or are followed by the to-infinitive:

be able
have
dare
need
ought
used

They are able to help
I have to confess
She didn't dare to tell me
I need to go
We ought to arrive on time
I used to enjoy tennis

with adverbials using too and enough

These are common constructions:

I have more than enough work to do, thank you.
There's too much wrong with it to repair it.
We won't have enough money to spend.
There was too much noise to think properly.
It's too early to tell.

The confusion between to and too is an obvious issue but learners will also make errors such as
*I had enough spend
*She had too much work for leaving early
etc.

with how, where, when, what (but not why) and the verbs ask, enquire, explain, clarify, describe, see, recognise, identify, know, show, demonstrate, understand, realise

Other question words are followed by the to-infinitive with these verbs. See why above as the exception with the bare infinitive. See also tell, above.

Please tell me how to do this.
Do you know what to think of him?
They enquired where to pay.
I saw what to use it for.
I recognised when to shut up.
I identified where to install it.
I'll ask what to do.
I told them when to stop.
I don't understand how to work it.
I described how to get there.
I demonstrated what to do.
Show him where to put it.
I realised how to tell her.
I explained when to come and how to get in.

With exposure and a bit of practice, most learners have little trouble with this area. There is a temptation to avoid the structures, however, and produce clumsy sentences such as:

I demonstrated to him the way to work the coffee maker.
I didn't understand the method to do the calculation.
I didn't know the place to put it.
I asked him what was the time to come.

or even errors such as:

*I described the way coming to my house.
*I realised what was the problem to do it.
*Please show me how I am working it.

Related guides
the infinitive	this is the link to the in-service guide for this area
modal auxiliary verbs	for an essential guide to modal auxiliary verbs
gerunds and infinitives	an essential guide to this verb form with some contrast with the to-infinitive
finite and non-finite forms	for a much more technical guide to the infinitive and more in the in-service section

There's a short test to see if you can remember and recognise the uses of the infinitive.