Contrary to what some grammarians say, there is no rule against using split infinitives in English. One might use them with care, but splitting an infinitive is sometimes the best way to clearly express a thought.
What are split infinitives?
An infinitive is the uninflected form of a verb along with to—for example, to walk, to inflect, to split. A split infinitive is created by placing an adverb or adverbial phrase between the to and the verb—for example, to boldly go, to casually walk, to gently push. Although split infinitives have been widely condemned in grade-school classrooms, they’re common in writing of all kinds.
When you’re in doubt, avoiding the split can’t hurt, but don’t ruin a perfectly clear and natural-sounding sentence just to adhere to an arbitrary antisplitting rule.
When to avoid split infinitives
When moving the adverb to the end of a phrase doesn’t cause confusion or change the sentence’s meaning, it’s a good idea to keep the infinitive intact—for example:
He urged me to casually walk up and say hello.
There’s no reason why this sentence couldn’t be,
He urged me to walk up casually and say hello.
It’s also a good idea to avoid splitting infinitives too widely:
This software allows your company to quickly, easily, and cost-effectively manage all tasks.
One possible revision:
This software allows your company to manage all tasks quickly, easily, and cost effectively.
Sometimes, a split infinitive is simply more awkward than an alternative:
Do you have to so loudly play?
This sentence would be much less awkward as,
Do you have to play so loudly?
When to split infinitives
Infinitives should be split when the adverb either needs emphasis or wouldn’t work anywhere else in the sentence—for example:
They’re expected to gradually come down in price to about $50 to $75 each.
Placing gradually anywhere else in this sentence (They’re gradually expected … ; … come down in price gradually to about … ) would create awkwardness and confusion. Another example:
Caterpillar plans to more than triple employment at its four-year-old diesel generator plant in Newberry.
Here, the phrase more than would not work anywhere else in the sentence. Try it, and you’ll see.