Hands up. Who heard the rule “avoid split infinitives” before learning what an infinitive was? I’m certainly in that camp and I’m sure there are others there with me. It’s one of the rules that gets repeated frequently—even when those repeating it don’t know its provenance or purpose.
So what is a split infinitive? And should you actually avoid splitting them?
An infinitive is the base form of a verb. In English, that’s the form with to (to run, to walk, to feel etc.). A split infinitive occurs when you place another word, usually an adverb, between the to and its verb. Star Trek’s “to boldly go” is among the most famous split infinitives.
A Bit of History
The rule against split infinitives has been around for a long time. It comes from early grammarians forcing Latin grammar rules onto English. This doesn’t make a whole lot of sense since Latin infinitives appear as single words, so you can’t split them anyway. But hey, props to grammarians for trying to make sense of English, I guess.
The Chicago Manual of Style (CMOS) says that grammarians recommended avoiding splits between 1850 and 1925. Grammar Girl adds that this rule became especially prominent with Henry Alford’s The Queen’s English in 1865.
Yet, there’s plenty of evidence that split infinitives have been used throughout history (see the Oxford English Dictionary or the work of George O. Curme).
There’s also a long history of doubting this rule and showing leniency for split infinitives. For example, although E.B. White’s 1959 additions to The Elements of Style recommend avoiding splits, they make caveats for informal tone or emphasizing adverbs.
CMOS asserts that “it is now widely acknowledged that adverbs sometimes justifiably separate the to from the principal verb” (5.108). Justifications include adding emphasis to an adverb, clarifying meaning, or producing a natural sound (5.171). I’d argue that these justifications are also why split infinitives have never completely disappeared.
The AP Stylebook recommends avoiding splits under its (contested) split forms rule: “In general, avoid awkward constructions that split infinitive forms of a verb.” But the key words here are “awkward constructions.” The passage goes on to permit split verb forms and infinitives if they sound more natural or cannot be avoided.
The AMA Manual of Style says sometimes split infinitives provide greater clarity.
At this point, it seems that many style guides acknowledge this grammar rule by saying it’s not actually a rule or by giving enough leniency that it might as well not be.
So, Should You Avoid Split Infinitives?
Because “avoid split infinitives” remains stuck in people’s minds, there are some who will think splitting an infinitive is wrong. If you’re writing for such an audience, it might be worth avoiding splits. Indeed, authorities like Grammar Girl and Oxford recommend avoiding splits almost exclusively because some people are offended by them.
However, based on the shaky foundation of this norm and the fact that even in its heyday there’s evidence against a strong consensus on it, I don’t think avoiding the irritation of select prescriptivists is enough to warrant rewriting all split infinitives—especially in fiction where formal writing isn’t strictly necessary. So long as your sentences sound natural and don’t obscure meaning, I say go ahead and split your infinitives.