Capitalization in Titles of Works

Q. A coworker with a PhD in English lit comments that your example of title casing “Four Theories concerning the Gospel according to Matthew” isn't correct at all. “Concerning” and “according” are participles, not prepositions (thus these are participial, not prepositional, phrases). I've absolutely never seen “Gospel according to Anyone”—it's always “According to.” Thoughts? I'm not just nitpicking; trying to get a group of proofreaders and editors to pull together consistently on little stuff like this.

A. Gulp—a PhD in English lit? Well, here goes: Although “concerning” and “according” are participles, that doesn't stop them from forming prepositions. (You can confirm this in a dictionary.) In the title cited, “concerning” is a preposition with the object “Gospel,” and “according to” is a preposition with the object “Matthew,” so according to Chicago style they are lowercased. Many publishers follow a different guideline for title casing, however, by which all words over a certain length are uppercased, so it's not surprising if you see these prepositions uppercased in titles.