What is "split infinitive"

Split infinitive \Split infinitive\ (Gram.) A simple infinitive with to, having a modifier between the verb and the to; as in, to largely decrease. Called also cleft infinitive.

Note: The use of the split infinitive is commonly considered to be ungrammatical, but by most grammarians it is considered acceptible.

n. An infinitive with one or more modifiers inserted between the (term: to) and the verb.

n. an infinitive with an adverb between `to' and the verb (e.g., `to boldly go')

In the English language, a split infinitive or cleft infinitive is a grammatical construction in which a word or phrase comes between the to and the bare infinitive of the to form of the infinitive verb. Usually an adverb or adverbial phrase comes between them.

A well-known example occurs in the opening sequence of the Star Trek television series: " to boldly go where no man has gone before"; the adverb boldly is said to split the infinitive to go. Sometimes more than one word splits the infinitive, as in: "The population is expected to more than double in the next ten years".

In the 19th century, some grammatical authorities sought to introduce a prescriptive rule against it. The construction is still the subject of disagreement, though modern English usage guides have dropped the objection to the split infinitive.