Split infinitive

A split infinitive or cleft infinitive is an English-language grammatical construction in which a word or phrase, usually an adverb or adverbial phrase, comes between the marker to and the bare infinitive (uninflected) form of a verb. One of the most famous split infinitives occurs in the opening sequence of the Star Trek television series: to boldly go where no man has gone before. Here, the adverb "boldly" splits the full infinitive "to go." More rarely, the term compound split infinitive is used to describe situations where the infinitive is split by more than one word: The population is expected to more than double in the next ten years.

As the split infinitive became more popular in the 19th century, some grammatical authorities sought to introduce a prescriptive rule against it. The construction is still the subject of disagreement among native English speakers as to whether it is grammatically correct or good style. Henry Fowler wrote in 1926, "No other grammatical issue has so divided English speakers since the split infinitive was declared to be a solecism in the 19c: raise the subject of English usage in any conversation today and it is sure to be mentioned." However, most experts on language now agree that the split infinitive is sometimes appropriate. Those who use it consciously may see it as a form of hyperbaton, and some major poets have employed this to good effect.