Q. Some guides say not to begin a sentence with an abbreviation unless it’s Mr., Dr., and the like. How about St. Paul? Do you recommend spelling it out?
A. Since Chicago doesn’t approve of abbreviations in running text, we would generally not begin a sentence with one, but we too make exceptions for words like Mr., Dr., and (yes) St., and would not spell them out. Acronyms, on the other hand, seem fine for launching a sentence, especially when the effort to avoid one looks worse.