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:
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.
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