In grammar, infinitive is the name for certain verb forms that exist in many languages. In the usual (traditional) description of English, the infinitive of a verb is its basic form with or without the particle to: therefore, do and to do, be and to be, and so on are infinitives. As with many linguistic concepts, there is not a single definition of infinitive that applies to all languages. Many Native American languages and some languages in Africa and Aboriginal Australia simply do not have infinitives or verbal nouns. In their place they use finite verb forms used in ordinary clauses or special constructions.
In languages that have infinitives, they generally have most of the following properties:
• In most uses, infinitives are non-finite verbs.
• They function as other lexical categories — usually nouns — within the clauses that contain them, for example by serving as the subject of another verb.
• They do not represent any of the verb's arguments (as employer and employee do).
• They are not inflected to agree with any subject
• They cannot serve as the only verb of a declarative sentence.
• They do not have tense, aspect, moods, and/or voice, or they are limited in the range of tenses, aspects, moods, and/or voices that they can use. (In languages where infinitives do not have moods at all, they are usually treated as being their own non-finite mood.)
• They are used with auxiliary verbs.
However, it bears repeating that none of the above is a defining quality of the infinitive; infinitives do not have all these properties in every language, as it is shown below, and other verb forms may have one or more of them. For example, English gerunds and participles have most of these properties as well.
Infinitives in English
English has three non-finite verbal forms, but by long-standing convention, the term "infinitive" is applied to only one of these. (The other two are the past- and present-participle forms, where the present-participle form is also the gerund form.) In English, a verb's infinitive is its unmarked form, such as be, do, have, or sit, often introduced by the particle to. When this particle is absent, the infinitive is said to be a bare infinitive; when it is present, it is generally considered to be a part of the infinitive, then known as the full infinitive (or to-infinitive), and there is a controversy about whether it should be separated from the main word of the infinitive. (See Split infinitive.) Nonetheless, modern theories typically do not consider the to-infinitive to be a distinct constituent, instead taking the particle to to operate on an entire verb phrase; so, to buy a car is parsed as to [buy [a car]], not as [to buy] [a car].
The bare infinitive and the full infinitive are mostly in complementary distribution. They are not generally interchangeable, but the distinction does not generally affect the meaning of a sentence; rather, certain contexts call almost exclusively for the bare infinitive, and all other contexts call for the full infinitive.
Huddleston and Pullum's recent Cambridge Grammar of the English Language (CGEL) does not use the notion of the infinitive, arguing that English uses the same form of the verb, the plain form, in infinitival clauses that it uses in imperative and present-subjunctive clauses.
Uses of the bare infinitive
The bare infinitive is not used in as many contexts as the full infinitive, but some of these are quite common :
• The bare infinitive is used as the main verb after the dummy auxiliary verb do, or most modal auxiliary verbs (such as will, can, or should). So, "I will/do/can/etc. see it."
• Several common verbs of perception, including see, watch, hear, feel, and sense take a direct object and a bare infinitive, where the bare infinitive indicates an action taken by the main verb's direct object. So, "I saw/watched/heard/etc. it happen." (A similar meaning can be effected by using the present participle instead: "I saw/watched/heard/etc. it happening." The difference is that the former implies that the entirety of the event was perceived, while the latter implies that part of the progress of the event was perceived.)
• Similarly with several common verbs of permission or causation, including make, bid, let, and have. So, "I made/bade/let/had him do it." (However, make takes a to-infinitive in the passive voice: "I was made to do it.")
• With the word why. So, "Why reveal it?"
• The bare infinitive is the dictionary form of a verb, and is generally the form of a verb that receives a definition; however, the definition itself generally uses a to-infinitive. So, "The word 'amble' means 'to walk slowly.'"
• The bare infinitive form is also the present subjunctive form and the imperative form, although most grammarians do not consider uses of the present subjunctive or imperative to be uses of the bare infinitive.
Uses of the full infinitive
The full infinitive (or to-infinitive) is used in a great many different contexts :
• Outside of dictionary headwords, it is the most commonly used citation form of the English verb: "How do we conjugate the verb to go?"
• It can be used like a noun phrase, expressing its action or state in an abstract, general way. So, "To err is human"; "To know me is to love me". (However, a gerund is often preferred for this — "Being is doing" would be more natural than the abstract and philosophical sounding "To be is to do.")
• It can be used like an adjective or adverb, expressing purpose or intent. So, "The letter says I'm to wait outside", or "He is the man to talk to", or "[In order] to meditate, one must free one's mind."
• In either of the above uses, it can often be given a subject using the preposition for: "For him to fail now would be a great disappointment"; "[In order] for you to get there on time, you'll need to leave now." (The former sentence could also be written, "His failing now would be a great disappointment.")
• It can be used after many intransitive verbs; in this case, it generally has the subject of the main verb as its implicit subject. So, "I agreed to leave", or "He failed to make his case." (This may be considered a special case of the noun-like use above.) With some verbs the infinitive may carry a significantly different meaning from a gerund: compare I stopped to talk to her with I stopped talking to her, or I forgot to buy the bread with I forgot buying the bread.
• It can be used after the direct objects of many transitive verbs; in this case, it generally has the direct object of the main verb as its implicit subject. So, "I convinced him to leave with me", or "He asked her to make his case on his behalf." However, in some cases, the subject of the main clause is also subject of the infinitival clause, as in "John promises Mary to cook", where the cook is John (the subject of the main sentence), and not Mary (the object).
• As a special case of the above, it can often be used after an intransitive verb, together with a subject using the preposition for: "I arranged for him to accompany me", or "I waited for summer to arrive."
When the verb is implied, some dialects will reduce the to-infinitive to simply to: "Do I have to?"
The infinitive with auxiliary verbs
The auxiliary verb do does not have an infinitive — even though do is also a main verb and in that sense is often used in the infinitive. One does not say *I asked to do not have to, but rather, either I asked not to have to or I asked to not have to (but see split infinitive). Similarly, one cannot emphasize an infinitive using do; one cannot say, "I hear him do say it all the time."
Nonetheless, the auxiliary verbs have (used to form the perfect aspect) and be (used to form the passive voice and continuous aspect) both commonly appear in the infinitive: "It's thought to have been a ceremonial site", or "I want to be doing it already."
The modal auxiliary verbs, can, may, shall, will and must are defective in that they do not have infinitives; so, one cannot say, *I want him to can do it, but rather must say, I want him to be able to do it. The periphrases to be able to, to have to and to be going to are generally used in these cases.
There is a specific situation in which the infinitive is used like an "impersonal future tense", replacing "will". This is done through the construction :
to be + "to" + bare infinitive
Grammatically, this is identical to the instructional "I am to wait outside" construction (above), but does not signify somebody having been issued an instruction; rather, it expresses an intended action, in the same way as "will". This "tense" is used extensively in news reports, eg. –
• The Prime Minister is to visit the West Bank (active)
• Aid is to be sent to war-torn Darfur (passive)
This "future infinitive" construction is interesting in that it only has a future aspect to it in situations where the speaker is significantly distanced from the event. In cases where the subject of the sentence is not quite as distanced from the speaker, then the same construction takes on a sense of instruction or necessity (as in "he is to wait outside", or "he is to go to hospital").
The same construction can be used in conditional clauses - If you are to go on holiday, then you need to work hard (or, conversely, if you want to...then you are to...).
The impersonality aspect comes from the fact that the emotionless verb to be is used in the place of the more usual modal verbs which would normally connect the speaker to the statement. In this way, statements are given weight (as if some external force, rather than the speaker, is governing events).
Conversely, however, the construction also provides an uncertainty aspect, since it frees the speaker from responsibility on their statement – in the phrase "John will go", for example, the speaker is almost advocating their certainty that John will, in fact, go; meanwhile, "the Prime Minister is to go" simply states the knowledge that the PM's going is in some way foreseen. (If John ends up not going, for example, the "will go" construction is negated, while the PM's "to go" construction would still hold true, since all it expresses is an expectation). In both cases, the knowledge is simply being reported (or pretends to be) from an independent source. In this sense, this impersonal to + verb construction can almost be seen as a fledgeling renarrative mood.
Verbs Followed by an Infinitive
agree, aim, appear, arrange, ask, attempt, be able, beg, begin, care, choose
condescend, consent, continue, dare, decide, deserve, detest, dislike, expect, fail, forget, get, happen, have, hesitate, hope, hurry, intend, leap, leave, like, long, love, mean, neglect, offer, ought, plan, prefer, prepare, proceed, promise, propose, refuse, remember, say, shoot, start, stop, strive, swear, threaten, try, use, wait, want, wish.