In English, the preposition to often precedes the infinitive form of a verb (for example: to be, to love, to run, to expectorate, and so on). Whereas in Latin, prepositions are always single words (e.g.: apud, juxta, propter, sine, etc.).
Several nineteenth-century grammarians, notably Henry Alford in A Plea for the Queen’s English (1864), railed against so-called “split” infinitives, constructions where a word or phrase comes between the preposition to and the infinitive verb (to ever be, to truly in your heart love, to swiftly run, to forcefully expectorate, and so on). They believed that the preceding to was not simply a prepositional marker but an actual part of the verb; they further believed that splitting up the to and the infinitive verb was grammatically incorrect.
They were, are, and forever more shall be wrong on both counts.
A moment’s reflection will show that to is not an essential, grammatical part of infinitive verbs. In many English sentences, having to before the infinitive is optional, for instance: “The teacher helped her students [to] write better thesis statements.” Those Victorian grammarians, dazzled by their deep knowledge of Latin, failed to see how their own language works.
There is, on the other hand, no rule requiring you to split every infinitive. In fact, split infinitives sometimes sound quite clumsy, particularly if the split is a wide one (for example: “We will attempt to quickly and with the highest level of professionalism possible respond to your request.”). But the option to occasionally split infinitives enables authors to precisely control nuances of rhythm and meaning in their sentences.
First-Rate Writers Split Infinitives
— William Faulkner, “My Grandmother Millard and General Bedford
Forrest and the Battle of Harrykin Creek”
“Hamilton from boyhood on was an overachiever, one who found it necessary to more than compensate for his feelings of inadequacy.”
— Peter R. Henriques, Realistic Visionary
“Milton was too busy to much miss his wife.”
— Samuel Johnson, Lives of the Most Eminent English Poets
“Its five-year mission: to explore strange new worlds, to seek out new life and new civilizations, to boldly go where no man has gone before.”
— Gene Roddenberry, Star Trek
“Some believed in the Commission’s scheme to arbitrarily and permanently confine (and thus deepen) the channel, preserve threatened shores, etc.”
— Mark Twain, Life on the Mississippi, chapter 28