65. Verbs that Mean “Must” or “Can”

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Clear roads allow vehicles to go fast

Clear roads allow vehicles to go fast

Ordinary verb equivalents of “must” and “can” link with either a following verb (with “to” or “-ing”) or an “action” noun

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VERB CHOICES FOR EXPRESSING NECESSITY AND ABILITY

Many people, if asked to name some verbs of necessity and ability, would probably think first of so-called “modal” verbs – SHOULD, MUST, HAVE TO, CAN, MAY and MIGHT – verbs considered to belong more to grammar than to vocabulary. However, these meanings, like so many others in grammar, can be expressed by ordinary vocabulary as well. The aim of this post is to show how ordinary verbs can express the meanings of necessity and ability, and to highlight a few problems to avoid in using them. For information about modal necessity verbs, see 129. Differences between Necessity Verbs.

The main ordinary verbs in question are:

Necessity Verbs

COMMAND, COMPEL, ENSURE, ENTAIL, FORCE, INVOLVE, MAKE, MAKE … NECESSARY, MAKE IT NECESSARY, MEAN, NECESSITATE, ORDER, REQUIRE, FORBID, HINDER, OBSTRUCT, PREVENT, PROHIBIT, STOP, TELL.

Ability Verbs

ALLOW, ENABLE, ENCOURAGE, FACILITATE, HELP, LET, MAKE … POSSIBLE, MAKE IT POSSIBLE, PERMIT.

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BASIC USE OF ORDINARY VERBS OF NECESSITY AND ABILITY

To use any of these verbs instead of a modal you must normally mention not only the event or situation that must/can happen, but also its purpose or cause, like this:

(a) Computer games ALLOW children to develop numerous skills.

(b) International travel REQUIRES a passport.

Modal verbs, by contrast, do not require a purpose or cause to be mentioned in this way, though one can be added if necessary by means of a preposition or conjunction, like this:

(c) (With computer games), children CAN develop numerous skills.

(d) (For international travel), one MUST have a passport.

The reason why the ordinary verb allow in (a) needs the cause to be mentioned is that the verb’s very meaning requires the cause to be its subject – and subjects cannot be dropped from sentences (see 12. Singular and Plural Verb Choices). Most other ordinary verbs of necessity and ability are the same.

Ordinary verbs of necessity and ability belong to the wider class of cause-result verbs which are discussed in some detail in the post 32. Expressing Consequences. What makes them special is that they add to the basic cause-result meaning; ability verbs add the meaning of “can”, so that choice concerning the result is communicated as well as the result itself, while necessity verbs add the meaning of “should” or “must”, so that reduced choice concerning the result is understood. Ordinary cause-result verbs, such as CAUSE, LEAD TO and BRING ABOUT, suggest neither of these meanings – and are not the focus of this post.

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GRAMMAR STRUCTURES AFTER ORDINARY VERBS OF NECESSITY AND ABILITY

Must and can always need another verb, usually written straight after them – e.g. can develop in (c). Their ordinary-verb equivalents, however, do not always need an ordinary verb after them, but they can always have one if so desired. The next section examines how ordinary verbs of necessity/ability combine with a following verb, while the one after considers alternatives to using a second verb.

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1. Use of Second Verbs

The verb after allow in (a) is in the to (infinitive) form (to develop); but other second verbs need -ing instead. The choice depends on the particular verb of ability or necessity being used. The requirements are as follows (the underlined verbs belonging to both lists):

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Verbs Needing an Infinitive

ALLOW, COMMAND, COMPEL, ENABLE, ENCOURAGE, FORCE, HELP, LET (without to), MAKE IT POSSIBLE, PERMIT, FORCE, MAKE (without to), MAKE IT NECESSARY, ORDER, REQUIRE, TELL, FORBID.

For more on the common error of using to after MAKE, see 10. Words with Unexpected Grammar 1. A major point regarding all of the verbs is that, unlike in some other languages, there must usually be a noun before a following infinitive. It is incorrect to say *enables to succeeed instead of enables (someone) to succeed, and it would be incorrect to drop children from sentence (a) above. Similar errors are considered in the post 8. Object-Dropping Errors. The only exceptions are make it necessary and make it possible, where the word it makes a following noun unnecessary (though one could be added after for).

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Verbs Needing “-ing”

ALLOW, ENCOURAGE, FACILITATE, MAKE … POSSIBLE, PERMIT, ENSURE, ENTAIL, INVOLVE, MAKE … NECESSARY, MEAN, NECESSITATE, REQUIRE, FORBID, HINDER, OBSTRUCT, PREVENT, STOP.

As mentioned above, the underlined verbs in this list, like REQUIRE, are also in the previous list. However, their use with to and -ing is slightly different: with -ing they must have no noun in between; if you want to have a noun, you must use to. Consider this example:

(e) Travel to another country usually REQUIRES a passport … .

Because the noun a passport is written immediately after requires, only the infinitive of a verb is correct, e.g. to be shown. Without this noun, on the other hand, we would have to say requires showing a passport.

In contrast, the nouns that take only -ing, like INVOLVE, may or may not have a noun in between:

(f) Good practice INVOLVES (researchers) recording everything said.

(g) Creating time for study ENTAILS (learners) making sacrifices.

The verb MAKE … NECESSARY is the only exception: it cannot ever have a noun before the -ing verb. On the other hand, two verbs that nearly always have a noun there are HINDER and PREVENT. The preposition from can be optionally added:

(h) Leaving no time for study can prevent one/people/students (from) passing exams. 

It is worth noting, finally, that some -ing verbs can have a possessive noun (see 58. Optional Apostrophe Endings) or adjective just before them instead of an ordinary noun. For example, in (g) and (h) one could use learners’ and one’s.

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2. Using a Noun Equivalent of a Second Verb

Nouns with the same action meaning as verbs are examined in detail in such posts as 14. Action Outcomes,  31. Objects of Noun Actions and 131. Uses of “Action” Nouns. Examples are movement (from MOVE), creation, reversal, discovery, pretence and change (same spelling as the verb). Nouns of this kind can be used after most of the listed verbs above in place of a second verb in the to or -ing form, like this: 

(i) Computer games allow the development of numerous skills (by/in children). 

This possibility is useful to know if you are not sure whether -ing or to is correct. The only verbs that do not allow it are COMMAND, COMPEL, LET, MAKE and TELL, while MAKE IT NECESSARY/POSSIBLE needs to drop IT.

Sentence (i) also shows that using a noun equivalent of the second verb removes the need of to verbs to have a noun before them. However, this noun can still be mentioned if so desired after a preposition (by/in children above). Now here are some more examples. How would they be worded if the underlined nouns were verbs instead? 

(j) Noun use enables (the) omission of the subject of the second verb.

(k) Height restrictions on heavy vehicles prevent (the) disturbance of residential neighbourhoods.

(l) Failure to declare restricted goods will necessitate their confiscation by customs officers.

A verb in (j) would have to have to (with a noun before it). It could be either passive (… the subject … to be omitted) or active with a subject like writers (… writers to omit …). A verb in (k) would need -ing with a noun before it. Again the passive is possible (… neighbourhoods [from] being disturbed) or active (… them [from] disturbing …). A verb in (l) would also need -ing. It could be passive (… them/their being confiscated by …) or active (… officers confiscating them).

Finally, it sometimes happens that an ordinary verb of necessity or ability has nothing more than a non-action noun after it, for example requires a passport in (e) or entails sacrifices in (g). All of the listed verbs seem to allow this except COMMAND, COMPEL and TELL (which have a different kind of meaning when followed by an ordinary noun). When it happens, I feel that the meaning of an action word (showing and making in the examples) is still recognisable – it is just unmentioned because it is obvious.

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THE SPECIAL USE OF mean AND ensure

Two necessity verbs, MEAN and ENSURE, are typically joined to a second verb with that, like this:

(k) Using a spell check will mean/ensure that most spelling errors are discovered.

One of the verbs, MEAN, sometimes has -ing instead (means discovering). Happily, both verbs also allow a noun equivalent of the verb after them – in this case discovery – so that the need to find the right verb form can be avoided.

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