What’s a split infinitive? Let’s start with what an infinitive is. It’s the irreducible form of a verb, composed of two words, to and the infinitive form of the verb. Examples: to run, to swim, to party, to study. All of any verb’s other forms derive from the infinitive.
The old rule, invented in the nineteenth century, was never to split an infinitive—that is, never to put a word between the to and the verb. If I’d written the previous sentence this way, I’d have split an infinitive: “the old rule . . . was to never split an infinitive.” What’s wrong with that split infinitive? Arguably, nothing. But some split infinitives could be awkward and worthy of avoiding. If I wrote “To be or to not be, that is the question”—a famous line from Shakespeare’s Hamlet—you’d shiver because you’re used to hearing it without the infinitive split. That’s one reason not to split it. Another would be this: if what you put between to and the infinitive form of the verb were long and / or awkward. Here’s an example: “He wanted to deliriously and infinitely be happy.” The gap between to and the verb is too wide, and those adverbs are too clumsy to be inserted where they are. The sentence’s syntax is, bottom line, inelegant, and inelegance is to be shunned.
My undergraduate advisor for my English major would—honest to God!—stop me in mid-sentence if I so much as spoke a split infinitive. Yes, spoke. I became so self-conscious and hyper-aware of possibly making that mistake that I began monitoring myself beyond the bounds of reason. Truly, a split infinitive isn’t that big a deal.
Today, many fine writers, scholars, and teachers, will tell you to split an infinitive if not doing so would be more awkward than doing so. Conservative grammarians (prescriptivists) will disagree. I concur with the first group. Although my ears still recoil from the opening of the old Star Trek series, whose intonations include the phrase “to boldly go where no man has gone before . . .,” I’d argue that the more objectionable element in that utterance is the sexist use of man. Still, I became conditioned to wince at that putative error when I was busily listening to myself in college, and, to tell the truth, I’d rather be alert to my options by recognizing a split infinitive when I meet one than remain ignorant of what the heck that term means and why it could prove important. In the last analysis, audience is key. If I’m writing to an intellectually or academically conservative readership, my infinitives will remain intact.