A. Dear Grammar Geekess, CMOS has not, since the thirteenth edition (1983), frowned on the split infinitive. (For the latest, see CMOS 5.108.) In this day and age, it seems, an injunction against splitting infinitives is one of those shibboleths whose only reason for survival is to give increased meaning to the lives of those who can both identify by name a discrete grammatical, syntactic, or orthographic entity and notice when that entity has been somehow besmirched. Many such shibboleths—the en dash, for example—are worthy of being held onto. But why tamper with such sentences as the following?
Its five-year mission is to explore new worlds, seek out new life and new civilizations, to boldly go where no man has gone before.
His first thought, when something went wrong, was to immediately hit the escape key—even when he was nowhere near a computer.
It seems to me that, at least given these two examples, euphony or emphasis or clarity or all three can be improved by splitting the infinitive in certain situations. It’s one of the advantages of a language with two-word infinitives. One might observe, for that matter, that English infinitives are always split—by a space. Sincerely, Editor (grammar god [or more probably warlock], filling in for the goddesses)
[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]