An infinitive verb form with an element, usually an adverb, interposed between to and the verb form, as in to boldly go.Usage Note:
The split infinitive has been present in English ever since the 14th century, but it was not until the 19th century that grammarians labeled and condemned the usage. The only rationale for condemning the construction is based on a false analogy with Latin. The thinking is that because the Latin infinitive is a single word, the equivalent English construction should be treated as if it were a single unit. But English is not Latin, and distinguished writers have split infinitives without giving it a thought. Noteworthy splitters include John Donne, Daniel Defoe, George Eliot, Benjamin Franklin, Abraham Lincoln, William Wordsworth, and Willa Cather. Still, those who dislike the construction can usually avoid it without difficulty. The sense of the sentence To better understand the miners' plight, he went to live in their district
is just as easily expressed by To understand the miners' plight better, he went to live in their district.
However, one must take care not to ruin the rhythm of the sentence or create an unintended meaning by displacing an adverb. • When choosing to retain split infinitives, one should be wary of constructions that have more than one word between to
and the verb. The Usage Panel is evenly divided on the one-adverb split infinitive. Fifty percent accept it in the sentence The move allowed the company to legally pay the employees severance payments that in some cases exceeded $30,000.
But only 23 percent of the panel accepts the split infinitive in the sentence We are seeking a plan to gradually, systematically, and economically relieve the burden.
In some contexts, the split infinitive is unavoidable, as in the sentence We expect our output to more than double in a year.
• Excessive zeal in avoiding the split infinitive may result in an awkward placement of adverbs in constructions involving the auxiliary verbs be
Infinitive phrases in which the adverb precedes a participle, such as to be rapidly rising, to be clearly understood,
and to have been ruefully mistaken,
are not split and should be acceptable to everybody. By the same token, there are no grounds for objecting to the position of the adverb in the sentence He is committed to laboriously assembling all of the facts of the case.
What is “split” here is not an infinitive but a prepositional phrase.