Other than the use of the serial comma, perhaps no other style guideline causes more contention among writers and editors as that of how many spaces to use after a period.
Several weeks ago, I wrote about 10 writing pet peeves. Among them was content written with two spaces after a period. I always use the find-and-replace feature to change two spaces to one in documents that I edit.
My insistence on one space after a period (or question mark or the dreaded exclamation point) touched off a barrage of comments from PR Daily readers. Many insisted that one space after a period is just a preference and that two spaces makes content easier to read. Others quoted style guides—such as the AP Stylebook—that clearly state: “Use a single space after a period at the end of a sentence.”
James Felici—author of The Complete Manual of Typography—calls this “the debate that refuses to die … In all my years of writing about type, it’s still the question I hear most often, and a search of the web will find threads galore on the subject.” (1)