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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
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 can also be expressed quite easily with ordinary vocabulary (a not uncommon phenomenon in English: see 298. Grammar Meanings without Grammar). This post surveys the ordinary verbs that can express necessity and ability, and highlights a few problems to avoid in using them. For some special uses of their modal verb equivalents, see 237. Auxiliary Verbs in Professional Communication.
The main ordinary verbs in question are:
Necessity Verbs
COMMAND, COMPEL, ENSURE, ENTAIL, FORCE, IMPEL, 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, LEAVE, 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), a passport MUST be carried.
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 rather than the allowed or compelled person/ thing 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.
Most ordinary verbs of necessity and ability belong to the wider class of cause-result verbs discussed in some detail in this blog in 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, ability or permission concerning the result is communicated along with the result itself (see 181. Expressing Possibility), 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 another 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.
1. Using a Second Verb
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):
Verbs Needing an Infinitive
ALLOW, COMMAND, COMPEL, ENABLE, ENCOURAGE, FORCE, HELP, IMPEL, LEAVE, LET (without to), MAKE IT POSSIBLE, PERMIT, FORCE, MAKE (without to), MAKE IT NECESSARY, ORDER, REQUIRE, TELL, FORBID.
Although dropping to from an infinitive after LET is not usually difficult to remember, the similar need after MAKE often is (see 141. Ways of Using MAKE and 10. Words with Unexpected Grammar 1, #a).
A major point regarding the list as a whole is that, unlike in some other languages, there must usually be a noun (or equivalent) before a following infinitive: it is incorrect, for example, to say *enables to succeed instead of enables (someone) to succeed, and it would be incorrect to drop children from sentence (a) above. For more on this error, see 214. Test your Command of Grammar 2. The need for an object means these verbs belong to the larger group discussed in detail in this blog in 208. Verbs with an Object + Infinitive (see especially #1 and #7).
MAKE IT NECESSARY and MAKE IT POSSIBLE do allow a directly-following infinitive because the word it fulfils the need for an object. An extra noun can still be added if needed in a for phrase. For more about MAKE IT NECESSARY / POSSIBLE, see 190. Special Uses of “it”, #2.
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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 indicated above, the underlined verbs in this list are also in the previous one (note that FACILITATE is not underlined, despite its meaning similarity to HELP: see 250. Synonym Pairs with Contrasting Grammar 1, #5). Verbs allowing either -ing or to combine slightly differently with each: with -ing they must have no noun in between; to have a noun, they require to. Consider this:
(e) Travel to another country usually REQUIRES a passport… .
Because the noun a passport is written immediately after requires, only the infinitive of a following verb is correct, e.g. to be shown. Without a following noun, on the other hand, we would have to say requires showing a passport (see 292. Synonym Pairs with Contrasting Grammar 2, #5).
In contrast, most of the verbs that take -ing rather than to, 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.
With FACILITATE, a possessive noun or no noun at all is more common before -ing than a simple noun (see the end of 232. Nouns with an Object + “-ing”). On the other hand, HINDER and PREVENT are especially likely to need a simple noun before -ing. The preposition from can optionally be added after it:
(h) Leaving no time for study can prevent one/ people/ students (from) passing exams.
HINDER and PREVENT are additionally usable with a possessive rather than simple noun, e.g. one’s in (h). Possessives are also an option with some of the other -ing-requiring verbs, such as ENTAIL in (g).
The verbs MAKE…NECESSARY and MAKE…POSSIBLE act slightly differently from the others in requiring any added subject of their -ing verb to come at the end after for: makes VERBing necessary/ possible (for NOUN).
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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 31. Prepositions after “Action” Nouns 1, 131. Uses of “Action” Nouns and 280. Alternative Meanings 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 some 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
Although some of the above-mentioned verbs – ENTAIL and REQUIRE, for example – are sometimes joined to a second verb with that, there are two necessity verbs, MEAN and ENSURE, that are much more typically joined in this way:
(k) Using a spell check will mean/ ensure that most spelling errors are discovered.
MEAN sometimes has -ing instead of that (means discovering). For more about ENSURE, see 296. Tricky Word Contrasts 12, #1.
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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