In a course I am currently taking, this subject came up and I thought I would throw it out here too for any of you to add a comment to, should you care to...
I have to jump into the fray on this as I can relate to the “MUST have two spaces between sentences” v. “MUST have one space.”
I was “helping” my son with a high school paper a few years ago, and I told him per APA (Publication manual of the American Psychological Association, 2010) and MLA (The MLA Center, 2016) one or two spaces is acceptable. He was marked down for using two spaces and his high school teacher said "two spaces is no longer acceptable."
So today I searched it out again and for MLA it says, "Leave one space after a period or other concluding punctuation mark, unless your instructor prefers two spaces" (2016). For APA it explicitly states, “one space after periods” (2010, p. 87) then on the next page states, “Spacing twice after punctuation marks at the end of a sentence aids readers of draft manuscripts” (2010, p. 88). So, for a final draft it should be a single space after a period ending a sentence, if I am reading the manual correctly. For the type of work we are doing for these modules, is it left up to the judgment of the professor? Perhaps there is another reference in the APA manual I have not seen yet? I am still a bit confused by this debate. At the risk of using a little colloquialism, is this a hill we/I need to die on?
Publication manual of the American Psychological Association. (2010). Washington, DC: American Psychological Association.
The MLA Style Center. (2016, July 27). Retrieved from https://style.mla.org/number-of-spaces-after-period/