A split infinitive puts a word — almost always an adverb — between "to" and the verb it belongs to. "To boldly go" is the most famous example: "boldly" splits "to go."
Like the preposition-at-the-end myth, this one comes from 19th-century grammarians modeling English on Latin, where the infinitive is a single word and physically can't be split. English infinitives are two words ("to" + verb), so there's nothing structurally stopping something from going between them — the rule was imported from a language where the situation doesn't even apply.
Often, splitting the infinitive is simply the more natural place for the adverb, and moving it elsewhere creates an awkward or ambiguous sentence.
In very formal writing, some readers still treat split infinitives as an error even though modern style guides don't. If you're writing for an audience or publication with strict traditional conventions, it's reasonable to avoid splitting just to sidestep the objection — not because the sentence is actually wrong, but because some readers will flag it regardless.
Put the adverb wherever it reads most naturally and clearly. If splitting the infinitive produces the smoothest sentence — which it usually does — split it. This isn't a grammar violation; it's a 150-year-old style preference that most contemporary style guides (including Fowler's and the Chicago Manual of Style) explicitly say is fine to ignore.
Check your writing →
Proofread Bot