An infinitive consists of to plus the base form of a verb: to think, to breathe, to dance. When a modifier appears between to and the verb, an infinitive is said to be “split”: to carefully balance, to completely understand.

When a long word or a phrase appears between the parts of the infinitive, the result is usually awkward.

Attempts to avoid split infinitives can result in equally awkward sentences. When alternative phrasing sounds unnatural, most experts allow—and even encourage—splitting the infinitive.

At times, neither the split infinitive nor its alternative sounds particularly awkward. In such situations, it is usually better not to split the infinitive, especially in formal writing.