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Concourse 2

The infinitive

infinite

In the initial plus section of this site, there is an essential guide to the infinitive which explains what it 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.

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 verbs is to consider whether or not they are followed by the bare or the to-infinitive.
Like this:

Pure modal auxiliary verbs
can | could | may | might | shall | should | will |would | must | ought to
Semi-modal auxiliary verbs
used | need | dare
Marginal auxiliary modal 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 verb.  That is not the view taken on this site because in most other respects the verb is a pure modal, 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.

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 modal auxiliaries listed above.

When we look at the semi-modal 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 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:


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
    2. Other verbs, 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 or a view based on past experience, when 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 rare or forbidden.
  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, compel, encourage, force, help, instruct, invite, oblige, order, permit, persuade, press, recommend, request, remind, show (how), teach, tell, tempt, warn (not)

† 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 hear that the bell is broken
not
    *I hear the bell broken
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

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:


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
    3. deontic adjectives include:
      wrong, right, crazy, important, necessary, good, bad, essential, unnecessary
    4. dynamic adjectives include:
      easy, difficult, hard, simple
  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 they include:
      glad, surprised, happy, pleased, delighted, sorry, willing, concerned, disappointed, mortified, astonished, unhappy, anxious and more

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:


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
  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.

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 preposition 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:

The single complication is that the infinitive can follow an adjective or a noun phrase and that is something not paralleled in many languages.


where

The passive after wh- words and impersonal pronouns

he told us where to go  

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 much more uncommonly used this way.

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 the writer / speaker's 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
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


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