The Editor’s Manual
Free learning resource on English grammar, punctuation, usage, and style.
English has the “to”-infinitive (or full infinitive) and the bare infinitive. The “to”-infinitive can also appear as a split infinitive.
An infinitive (e.g., “to go”) is split when a word appears between “to” and the verb (“to not go”). It is fine to split the infinitive in English.
Split infinitives are grammatically fine in English. Splitting an infinitive can help clarify meaning and emphasize the right word (e.g., “I promise to always be there for you”).