Split infinitives should be avoided in formal writing. In formal writing, it is considered bad style to split an infinitive, but in more informal writing or in speech this has become more acceptable.

What is the rule about splitting infinitives?

To split an infinitive is to put a word or words between the infinitive marker—the word to—and the root verb that follows it. A common example is the Star Trek phrase “to boldly go.” Here, the infinitive to go is split by the adverb boldly.

What is an example of a split infinitive?

What's a split infinitive then? A split infinitive is when other words creep into the middle of an English infinitive. The most famous example is Star Trek's “to boldly go where no one has gone before”.