Sometimes infinitives need a little space. A split infinitive occurs when there’s an adverb between two parts of an infinitive. An infinitive consists of the word to and the simple form of a verb (e.g. to go and to read). “To suddenly go” and “to quickly read” are examples of split infinitives because the adverbs (suddenly and quickly) split (or break up) the infinitives to go and to read.
Infinitives as Nouns
While infinitives look like verbs, they often function as nouns. For example, in the sentence “The man wants to eat dinner,” the infinitive “to eat” looks like a verb, but it actually functions as a noun. It names the thing that the man wants rather than naming what he’s doing.
The most important thing to remember about infinitives is that they form a single thought, action, or idea. For this reason, infinitives should generally be kept together rather than “split” apart.
When to Split an Infinitive
While the general rule in English grammar is to avoid split infinitives, most grammar experts agree that they’re acceptable under certain circumstances. In fact, sometimes they can even be preferable to awkward phrasing that makes a sentence unclear.
Take the following sentence: “The Board of Education decided to carefully evaluate each student’s performance.” In this sentence, the infinitive to evaluate is split by the adverb carefully. Changing the sentence to read “The Board of Education decided carefully to evaluate each student’s performance,” is misleading, as carefully seems to describe decided rather than to evaluate. At the same time, changing the sentence to read “The Board of Education decided to evaluate carefully each student’s performance,” is both awkward and a bit unclear. In this case, then, the best way to convey the meaning of the sentence is to split the infinitive.
Split infinitives are common in spoken and informal English. It wasn’t until the 1800s that the act of splitting infinitives began to be considered grammatically incorrect. Nevertheless, in formal writing, it’s best to avoid splitting infinitives. To do this, try to place adverbs either before or after the phrases they modify whenever possible.