Q. What is the CMOS stance regarding the use of numerals for a year at the beginning of the sentence? For example, “1980 was indeed a good year.” I see that AP allows it, but I don’t know if you do.
A. CMOS still considers spelling out a year at the beginning of a sentence to be the better option. If the result is awkward, as it often is with a year, the recommendation is to reword: The year 1980 was indeed a good one. This rule is an editorial nicety; a numeral isn’t as effective as a capital letter at signaling the start of a new sentence. In other words, it’s a rule you can break in all but the most polished, CMOS-approved prose—for example, you can ignore it in casual correspondence or where space is at a premium (or if you follow AP style!). See CMOS 9.5, which says that an exception may be made for years “if necessary.”