Q. Hello: When using title case (CMOS 8.160), does a participial preposition (CMOS 5.181) appear in lowercase or does it get initial caps? Thanks very much.
A. The terms listed in 5.181 (assuming, barring, concerning, considering, during, notwithstanding, owing to, provided, regarding, respecting, and speaking of) are all longer than four letters, so they’d get initial caps under Chicago’s latest rules for title case. But other than to and of, those words are participles, not prepositions, so they’d be capped regardless (whereas to and of would remain lowercase).