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Concourse 2

The infinitive in English

infinite

The title of this guide deliberately refers to in English.  Some languages, such as Modern Greek, Japanese and a range of other languages have nothing that is recognisably an infinitive and in other languages, the base form of a verb plays no grammatical role.
It is unsurprising that learners of English, especially from those language backgrounds, have some difficulty understanding the concept of an infinitive and using it successfully.
In many other languages, including many European ones, a single form of the verb does service as the equivalent of the English bare infinitive, the infinitive with to and the -ing form of a verb.

define

Definition

In the initial plus section of this site, there is an essential guide to the infinitive which explains what the infinitive is and how it is used.  The assumption here is that you already understand the distinction between bare and to-infinitives and between finite and non-finite verb forms but a rapid reminder may be helpful:

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.

The word infinitive, incidentally derives from the Latin meaning, roughly, unlimited and that is the clue to its nature – the infinitive is not limited by person, tense or number.  It just is.

This guide covers the main ways in which the infinitive is used in English (whether bare or with to).

open

Infinitives and modal auxiliary verbs
You can go now  

This is probably the most common use of the infinitive in English and the first use that most learners encounter.  This is not the place to consider all the possible meanings and uses of the infinitive with modal auxiliary verbs but it is worth noting that one usual distinction between pure and semi-modal auxiliary verbs is to consider whether or not they are followed by the bare or the to-infinitive.
Like this:

Pure or central modal auxiliary verbs Infinitive form
can | could | may | might | shall | should | will |would | must | ought to Followed by the bare infinitive, e.g., go
Semi-modal auxiliary verbs Followed by the to infinitive, e.g., to go
used | need | dare
Marginal modal auxiliary verbs
happen | care | mean | seem | tend | turn out | be about | be likely | be supposed

It is fairly easy to spot the rogue here.  It is the verb ought which, because it is followed by the to-infinitive, is often classified as a semi-modal auxiliary verb.  That is not the view taken on this site because in most other respects the verb is a central or pure modal auxiliary verb, having no truly lexical form in the way that semi-modal auxiliary verbs do.
There is more on all of this linked in the list of related guides at the end (follow the link to the modality index).

What is less easy to notice from the list above is the colligational nature of some of the verbs.

We can, for example, have both:
    They can do the work
and
    The work can be done
so both active and passive uses of the infinitive are acceptable.
The same applies to all the other pure or central modal auxiliary verbs listed above.

When we look at the semi-modal auxiliary verbs, the following are acceptable:
    They used to do the work
    The work used to be done
    They needed to do the work
    The work needed to be done
but with the semi-modal auxiliary verb dare, the passive use of the infinitive is not acceptable:
    They dared tell the teacher
    *The teacher was dared to be told.

With the marginal modal auxiliary verbs listed, the situation is more diverse and less clear cut:

clock

Tense, aspect and voice with the infinitive

The infinitive has just two tense forms:

  1. The present infinitive:
        I am happy to help
  2. The perfect infinitive
        I am happy to have helped

Both of these can take on aspectual meanings with progressive forms:

  1. The present progressive infinitive:
        I am happy to be helping
  2. The past progressive infinitive:
        I am happy to have been helping

These forms are subject to the same constraints and structural rules as the simpler form of the infinitive.

The guide to the passive, linked below, considers passive infinitives in some depth.  Here it will be enough to exemplify the two main forms:

  1. Present passive infinitive:
        I want to be invited
  2. Perfect passive infinitive:
        It should have been repaired

Both of these forms can be combined with the progressive aspect to make complex formulations such as:
    It needs to be being continuously oiled
    The machine should have been being serviced more often
but such forms are rare and of varying acceptability to some speakers.

let go

Catenative verbs
Let go!  

The verb catenate may be defined as join together in a series and, just like modal auxiliary verbs, there is a range of verbs in English which can be followed by a non-finite form.  That form may be the bare infinitive, the to-infinitive or the -ing form.  We are only concerned with the first two of these here.
Strictly speaking, catenative verbs are those in which the main verb is followed directly by the non-finite form with no intervening object so, for example
    I intend to go
    I like swimming
are true catenative structures but
    I want him to go
    She watched them playing
are not.
For the purposes of this guide we will ignore this technicality but the guide to catenative verbs linked in the list of related guides at the end, does not.

  1. Verbs which are followed directly by a bare infinitive are almost a closed set and the uses are quite rare.  The passive is almost impossible with any of these.  They include:
    1. let, as in, e.g.:
          Don't let go!
    2. make, as in e.g.:
          She made do with very little furniture
    3. help, as in, e.g.:
          Please help repair the table
    4. hear, as in e.g.:
          I hear tell he's quite rich
  2. Verbs which are followed by an object plus the bare infinitive are of two main sorts:
    1. verbs of physical (not mental†) perception.  These verbs refer to a single event rather than anything progressive or iterative and can often be used in the passive.  They include:
      1. I felt the ground move
      2. She heard the door open
      3. I noticed the car swerve
      4. They observed man break in
      5. I perceived the rain start
      6. I saw the man arrive
      7. I smelt the dinner burn
      8. I watched the man jump

        (When these verbs are followed by an -ing form they imply that the whole of an event was not perceived.  So for example:
            They observed the man breaking in
        implies that the action began before the observation and may have continued after it.
        Compare, too:
            I saw her sing at the opera vs. I saw her singing in the garden
            I smelt the dinner burn vs. I smelt the dinner burning
        and so on.
        For other examples, see the guide to finite and non-finite forms, linked below.)

    2. Other verbs, with the same structural characteristics including:
      1. The teacher had me do it again
      2. I helped her get up
      3. I let her go early
      4. I have known it be cold in April
      5. I made them stay late
  3. Verbs which are directly followed by the to-infinitive form a large group and many of them refer to the future rather than the past.  (When reference is to the past or to a view based on past experience, the -ing form is usually the form which follows.)
    1. These verbs include:
      afford, agree, aim, apply, arrange, attempt, care, chance, choose, condescend, consent, contrive, decide, decline, demand, deserve, determine, endeavour, expect, fail, happen, hasten, hesitate, hope, intend, learn, long, manage, mean, offer, prepare, pretend, proceed, profess, promise, refuse, resolve, seek, seem, strive, struggle, swear, threaten, trouble, undertake, volunteer, wait, want, wish.
    2. In nearly all cases, the verbs refer to a prospective rather than past action (but there are a few exceptions).
    3. None can be used with an intervening object, even when they are transitive so we allow, for example:
          He failed / struggled / swore / promised / wanted to pass the examination
      but not:
          *He failed / struggled / swore / promised / wanted the examination to pass.
    4. Passive uses are vanishingly rare or forbidden because no intervening object is present.
  4. Verbs which are followed by an object and the to-infinitive are rarer but can by their nature be used in the passive include:
    advise, allow, ask, beg, compel, encourage, forbid, force, get (=persuade), help, instruct, intend, invite, oblige, order, permit, persuade, press, recommend, request, remind, show (how), teach, tell, tempt, urge, warn (not)
    So, for example, we can have:
    Active form → Passive form
    I advised her to wait → She was advised to wait
    They compelled me to answer → I was compelled to answer
    She invited the vicar to come → The vicar was invited to come
    The man reminded me to attend → I was reminded to attend
    and so on
    Two of these verbs resist passive constructions so we do not usually encounter:
        The woman was got to answer
        The man was intended to help

† When the verb refers to metaphorical mental perception rather than physical perception, a that-clause is preferred.  For example:
Physical perception:
    I heard the bell ring
Mental perception
    I heard that the bell is broken
not
    *I heard the bell break
because that carries a different meaning of hear.
Physical perception:
    I felt the rain start
Mental perception:
    I felt that the rain will help the garden
not
    *I felt the rain help the garden

For fuller lists, see the guide to catenative verbs linked in the list of related guides at the end.

firework

The infinitive as the subject or object
To miss the fireworks would be crazy  

With catenative verbs the infinitive forms part of the object of the main verb but infinitives can also be nominalised to form the subject of a verb or be part of a nominalised non-finite clause.  The form is almost always marked in some way for emphasis and is much more frequent in spoken rather than written language.  For example:

Occasionally, a for-phrase may be inserted before the infinitive as in, for example:

Infinitive clauses can also post modify the subject noun and form part of a nominalised clause as the subject of the verb.  For example:

Nominalised infinitive constructions can also operate as the object of verbs, of course, and any transitive verb followed by the infinitive can be analysed as the verb plus a nominalised infinitive clause object as in, e.g.:
    I expected to go
    I chose to have the argument
    I want to see her
and that is not at all unusual.
All the uses of the infinitive with transitive verbs can be replaced by simple noun phrases so we can also have:
    I expected the bus
    I chose the silver car
    I want the money
It is worth commenting in passing that the -ing form is often referred to as a gerund (or, a somewhat different concept, a verbal noun) in expressions such as:
    I enjoy swimming
    I remember going to the game with her
etc.
If these forms are nouns (i.e., gerunds) then it makes sense, too, to refer to infinitive clauses as nouns in these circumstances.

difficult

The infinitive after adjectives
I was astonished to see the boat
and it was hard to see how it got there		  

There are two main sorts of adjectives which are followed by an infinitive, and it is always the to-infinitive which is used.  Simply telling learners that the bare infinitive does not follow an adjective may avoid a good deal of error.
The following are unmarked forms of some of the structures seen in the previous section.  Most of the clauses can be rephrased for marked meaning, i.e., emphasis, so we could have, for example:
    To see the difference is important
instead of the more normal, i.e., unmarked:
    It is important to see the difference

  1. Used with the dummy or anticipatory it:
    Many of these are modal adjectives, some epistemic (referring to possibility or likelihood) some deontic (referring to obligation) and some dynamic (referring to ability).
    1. The form is
          It + be + adjective + to-infinitive + object or other verb complement
      as in, for example:
          It is important to see the difference
          It is impossible to believe he can do it
    2. epistemic adjectives include:
      impossible, common, unusual, rare, possible, certain, likely, unlikely, normal.  For example:
          It is impossible to believe it
          It is certain to be her
          It is unusual to accept it
    3. deontic adjectives include:
      wrong, right, crazy, important, necessary, good, bad, essential, unnecessary.  For example:
          It is wrong to accept the money
          It is crazy to believe her
          It is essential to change the oil
    4. dynamic adjectives (referring to ability) include:
      easy, difficult, hard, simple.  For example:
          It is easy to believe her
          It is difficult to accept that
          It is hard to do it
  2. Used to describe someone's feelings:
    1. The form is
          Subject + copular verb + adjective + to-infinitive + object or other verb complement
      as in, for example:
          She is happy to come to the party
          They are reluctant to eat it
          They seem delighted to be here
    2. Many common adjectives work in this way and many represent some form of dynamic modality, in this case that of willingness.  They include:
      glad, surprised, happy, pleased, delighted, sorry, willing, concerned, disappointed, mortified, astonished, unhappy, anxious and more.  For example:
          I am glad to help
          She would be delighted to assist
          The were disappointed not to see her

Both types of structure exemplified here can be used in the passive although not all adjectives naturally so.  For example:

In particular, the adjectives frequently used with the anticipatory it are rare in the passive and often sound clumsy or plain wrong.  We would not normally accept, for example:

Passive infinitives are considered in much more detail in the guide to the passive.  You can open that section of the guide in a new tab by clicking here.

writing

The infinitive of reason or purpose
She wrote to ask how he was  

This is not an uncontroversial category because the sense of reason or purpose is often contained within the verb itself, and it may be argued that the use of to in these structures is better considered prepositional rather than part of the to-infinitive (hence its possible replacement with the complex preposition in order to).
However, for teaching purposes, the category is sometimes useful as, superficially at least, the structure is similar to the forms already considered.
Here, a few examples will do:

etc.

There are some complications:

  1. Negating the structures is more complicated because a sentence such as
        I sat in the shade not to get sunburnt
    is clumsy and usually replaced with
        I sat in the shade so as not to get sunburnt
    or
        I sat in the shade in order not to get sunburnt
  2. The verbs go and come are routinely followed by and rather than to, especially informally, so, we prefer
        Go and look
    to
        Go to look
    and
        Come and see
    to
        Come to see
  3. Slightly less acceptably to many people, and something deprecated in formal English, is the use of and with the verb try as in, for example:
        Try and help her
    rather than the more formally correct
        Try to help her
  4. The verb wait is frequently used with and rather than to as in, for example:
        Let's just wait and see
    but in this case, it is arguable that the meaning is different from
        Let's just wait to see
    because the former implies two actions following each other and the latter implies the reason for waiting.

Error alert:
The verbs come, get, grow, begin and start are often followed by a to infinitive but do not imply causality; they imply a sense of a gradual process.  So for example:
    I came to like her
does not allow an alternative with in order to and nor do:
    I got to know her
    I grew to enjoy the weather
    We began to lose touch
    We started to meet quite often

prohibit

The infinitive after be: prohibitions, orders and absolute arrangements
You are not to eat the apple  

A form that is almost unique to English (among European languages, at least) is the use of the infinitive after the verb be to signal absolute obligations and prohibitions.
The structure is formal and often used in notices and other written texts produced by those in authority.
Examples of the use are:
    Children are not to leave the premises unaccompanied
    Passengers are not to proceed beyond this point
    Officers are to be in uniform at all time
    Desks are to be kept tidy
    This door is to be kept clear of obstructions

An allied construction concerns the future, whether in the past and unfulfilled or prospective in sense.  The meaning is akin to the previous examples because the expression carries an implication of inevitability unusual for future forms in English.
Examples include:
    There is to be another meeting tomorrow.
    There was to be a rehearsal that afternoon but the director was ill
    We are to meet again tomorrow
    We were to see the boss the next day
and so on.

cold

The infinitive after too and enough
It was too cold to play  

Both these adverbs are routinely followed by the to-infinitive (and never by the bare infinitive).  They are often analysed as a subset of the previous category but that is mistaken because here it is rarely possible to use the complex subordinator in order to as an alternative.
Again some examples are enough because the structure is quite simple:

With this structure, negation is more straightforward.  For example:

There are some complications:

  1. The infinitive can follow an adjective or a noun phrase and that is something not parallelled in many languages.  For example:
        The food was good enough to eat
    or
        We took enough food to keep us going for the whole day
  2. Only the adverb enough can be used preceding a noun phrase so we allow:
        She had enough books to read
    but we do not allow
        *She had too books to read
  3. The adverb enough follows the adjective but precedes the noun (when it is a determiner, not an adverb) so we get, for example:
        The weather was nice enough to go for a walk
        The was enough rain to help the garden
  4. There is a formal use of enough following the noun phrase (again as a determiner) rather than preceding it as in, e.g.:
        There was rain enough to help the garden
        She had books enough to read
  5. The adverb too only precedes an adjective.  For example:
        The pie was too hot to eat
    not
        *The pie was hot too to eat
where

The infinitive after wh-words and impersonal pronouns
He told us where to go and how to get there  

All wh-words, apart from why, are frequently followed by the to-infinitive.  For example:

Of these, the first four, using how, what, when and where are the most frequent.  The words which and whose are less commonly used this way.
Although permitted in many languages, the word why may not, in English be followed by the infinitive with to.  We do not see, therefore:
    *She asked him why to do it
but that is allowed in many languages and is the source of some interlingual error.

The indefinite or impersonal pronouns -thing, -one and -body series with some-, any-, no- and every- are also frequently followed by the to-infinitive.  For example:

reported

The passive infinitive in reported speech
She wanted her question to be answered  

Up to now, the passive infinitive has been covered more or less as a footnote to the various sections but, in reported or indirect speech, especially in formal speech and writing, and especially when reporting questions and requests, it is quite common.
For example:

and so on.  The usual constraints regarding the passive, covered in the guide linked at the end apply, of course.

bored

The infinitive in disjuncts or conjuncts
To be honest, I'm a bit bored  

Disjuncts come in two flavours: they suggest to the hearer / reader how the speaker / writer wants to be understood (style disjuncts) or they show how the speaker / writer feels about the content of what is said or written (attitude disjuncts).
Infinitives sometimes perform this function.  For example:

Conjuncts also occur outside the main clause but instead of expressing style or attitude, they connect what has gone before or what follows what is being said or written.  Infinitives are sometimes used for this function as in, for example:


Related guides
infinitive: essentials a simpler guide in the initial training section
finite and non-finite forms for a guide to the whole area
reported speech essentials for the simple guide to this area
catenative verbs for the guide (mostly) to the use of the infinitive vs. the gerund
reported and indirect speech for the more detailed guide
adjectives for the guide to this word class
the passive for the guide to how and when the passive is used
adverbials for more about disjuncts and conjuncts
markedness to see how other forms of emphasis are achieved
indefinite pronouns for more on the some-, any-, no- and every- series of pronouns
the modality index from here you can find links to semi-modal and central modal auxiliary verbs and much else

References:
Chalker, S, 1984, Current English Grammar, London: Macmillan
McLeod, D, n.d., Practising English, Ramsgate, UK: Home Language International