Q. When I was working on my graduate degree in English, I was told by a professor that the rule had changed for plurals of numbers (written as numbers) and letters (3s rather than 3’s or As rather than A’s). For the past 15 years I have been teaching it that way. Another colleague just recently saw that rule change somewhere online. Our new textbooks, however, do not teach it that way. We are currently working on a new handbook and would like to know if the rule has been changed or not. Thanks.

A. Chicago style omits the apostrophe, but the thing about style is, there is no single great arbiter who makes rules that everyone follows. Different houses use different styles. Following a particular style allows a person to be consistent within a given document, but it really doesn’t matter which style you choose.