Q. Can you tell me when The Chicago Manual of Style changed from recommending two spaces after a period (or any other end-sentence punctuation) to a single space? I’m looking for a year and/or edition and also a reason.
A. As far as I can tell, the 14th edition of CMOS (1993) was the first to use a single space after a period in its illustration of a typed manuscript (fig. 2.1), although the rule does not appear to be stated in that edition. The rule is clearly stated at 2.9 of the 15th edition (2003). The change reflected a shift in typesetting practices.