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There are quite a lot of situations that make it possible or necessary to write an infinitive verb without “to”
THE POSSIBILITY OF DROPPING “to” FROM ENGLISH INFINITIVES
English language courses usually make it clear quite early on that “infinitive” verbs (those that lack an ending after to) are sometimes used without the to. A well-known occasion, for example, is after “modal” verbs like will, can, should and must. However, detailed surveys of all the situations where so-called “bare” infinitives are possible or necessary are much harder to find. It is this kind of survey that I am attempting in the present post, in the hope of resolving every possible uncertainty that readers might have about the use of bare infinitives. I will consider first situations where dropping to is optional, and then those where it is compulsory.
A preliminary point to note is that the to of infinitive verbs is not a preposition (see 3. Multi-Use Words and 35. Words Followed by “to -ing”). It normally helps to distinguish infinitives from other verbs without an ending, such as imperatives (see 128. Imperative Verbs in Formal Writing), subjunctives (see 118. Problems with Conditional “if”, #6), and plurals in the present simple tense (see 12. Singular & Plural Verb Choices).
Guinlist posts that give some attention to the use of ordinary to infinitives include 60. Purpose Sentences with “For”, 78. Infinitive versus Preposition after Nouns, 83. Adjectives before a “to” Verb, 105. Questions with a “to” Verb, 119. BE Before a “to” Verb, 183. Statements between Commas, 208. Verbs with an Object + Infinitive and 239. Noun Phrases Made with a “to” Verb.
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OPTIONAL BARE INFINITIVES
The to of an infinitive verb is most commonly optional when the infinitive is the second of a pair that are combined together by a suitable linking word. In most cases the linking word will be a conjunction, especially and:
(a) To paraphrase well, one has to comprehend and (TO) REMEMBER the source text.
The optionality of to before remember here is not surprising, given the way and generally in English allows repeated words to be dropped (see 36. Words Left out to Avoid Repetition and 174. Eight Things to Know about Conjunctions, #6). The conjunction than is another common one found with a dropped to:
(b) Children are often keener to play with their parents than (to) watch TV.
Note, though, that when than is combined with rather, keeping to is rare (see #3 below).
Situations where the to of an infinitive is optional but not linked to one used earlier are quite rare, but do exist. One kind begins with what or all (that):
(c) What / All (that) plants DO at night IS (to) absorb carbon dioxide.
This is a sentence type considered in depth in these pages in 145. Highlighting with “What” Sentences. It contains two verbs, DO and BE, the latter followed by an infinitive clarifying what DO means. The effect is to mark the infinitive verb’s meaning as the main information in the sentence. It is the to of such infinitives that is usually optional.
One other place where a bare infinitive is optional but not linked to an earlier infinitive with to is after the verb HELP and its object, like this:
(d) Nicotine chewing gum can help smokers (to) quit.
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COMPULSORY BARE INFINITIVES
There seem to be at least five situations where a bare infinitive must be used.
1. After Modal Verbs and DO
This familiar kind of bare infinitive is illustrated in such combinations as will know, can go, may be, must have and should say, where the first word is always a verb of the “modal” kind. The same need also exists after the non-modal auxiliary verb DO (e.g. does not think).
A small potential for confusion is with the “semi-modals” NEED and DARE, which in questions and negative statements allow a choice between use like ordinary verbs (with DO and to) and use like “modal” verbs (without them). Compare the following:
Use like Ordinary Verbs (with to)
Negative Statement: … DO(ES) not need/dare TO SAY
Question: DO(ES) … need/dare TO SAY?
Modal Use (without to)
Negative Statement: … need not/dare not SAY
Question: need/dare … SAY?
For more information about NEED within these pages, see 83. Adjectives before a “to” Verb (last section), 129. Differences between Necessity Verbs and 208. Verbs with an Object + Infinitive.
Although there is a choice between the modal and non-modal uses of DARE and NEED in negative statements and questions, the dropping of to in the modal use is still in a sense “compulsory”. This is because once a decision has been made to use NEED or DARE as a modal – for example by placing not after it instead of before in a negative statement, or a subject noun after it instead of before in a question – then there is no choice about dropping to from the following verb.
Sometimes the need for to to be dropped because of a modal verb even affects what sentences like (c) above, where there would normally be a choice regarding to. This happens when the DO after what includes a “modal” verb, e.g. can do or will do. In such cases the modal verb’s requirement for an absent to will affect not just DO but also the later infinitive, so that the choice there will disappear (… is absorb carbon dioxide).
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2. After the Object of Certain Verbs
Many “cause” verbs can be followed by an object that is also the subject of an infinitive verb placed immediately after it (see 208. Verbs with an Object + Infinitive, #7). An example is:
(e) Price increases usually CAUSE demand TO FALL.
Most verbs like cause in this example (ALLOW, ASSIST, ENABLE, LEAD etc.) require the following infinitive to have to. However, there are at least three exceptions: MAKE (= “cause by forcing”), LET (= “cause by allowing”) and HAVE (= “cause by organizing”).
Either MAKE or LET can replace cause in (e), but will need to fall to drop its to (see 10. Words with Unexpected Grammar 1, example (a), and 141. Ways of Using MAKE, #3). The use of causative HAVE is illustrated by the following sentence from 116. Rarer Uses of HAVE:
(f) It is desirable to have young children work in groups.
In addition to these three cause verbs, there are a few “perception” ones with a similar but not identical requirement:
(g) On SEEING the liquid CHANGE colour, turn off the heat.
Change is here a bare infinitive after the object of the perception verb seeing. Other perception verbs are FEEL, HEAR, LISTEN TO, NOTICE, OBSERVE, SENSE, SMELL and WATCH.
The infinitive is not the only verb form that can follow the object of a perception verb, but it is compulsory for expressing the particular meaning of a completed rather than ongoing action. The alternative form, for ongoing actions, is an -ing participle (see 231. Verbs with an object + “-ing”). Having -ing for a completed action instead of a bare infinitive would be a grammar error of the “invisible” kind (see 100. What is a Grammar Error?).
The verb HAVE with a later bare infinitive can mean not just “cause”, as indicated above, but also “suffer”, like this:
(h) Farmers can easily have pests eat(ing) their crops.
HAVE with this passive meaning resembles perception verbs, and like them it allows a choice between a following infinitive and -ing verb. In fact, even HAVE with the “cause” meaning allows the same choice: working is possible in (f) as well as work.
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3. After “Sooner than” and “Rather than”
Sooner than can be used as a preference-expressing conjunction:
(i) Many cyclists wear a silly-looking helmet sooner than RISK serious injury.
As with all conjunctions, a following verb is typical. However, this verb must always be a bare infinitive. Rather than is similar, except that it allows an -ing verb as an alternative to the infinitive (e.g. rather than risking above). The meaning of rather than is also wider: sometimes it is little more than that of the preposition instead of.
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4. After DO + “all”/”nothing” + except…
An example of this use is:
(j) The program does everything except monitor performance.
The main verb in such sentences must always be DO and must be accompanied by an expression (everything above) that means “all” or “none” (see 215. Naming Exceptions). It is the verb after this use of except (here monitor) that is usually a bare infinitive. An -ing form is an alternative when the main verb is in a continuous tense (is doing … except monitoring above).
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5. In Infinitival “Why” Questions
Questions using an infinitive verb are the focus of the Guinlist post 105. Questions with a “to” Verb. They are often just the question word and the verb, as in what to do(?), where to go(?) and whether to respond. Usually the infinitive verb needs to, but to must be dropped when the question word is why, as in why wait? and suggestions with why not…? (see 274. Questions with a Hidden Meaning, #3).
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