Ah, the old “One space or two?” question is alive and well. For various reasons, people still cling to the old rule learned in primary school and undergraduate courses: put two spaces between sentences. Mostly, it’s a hold-over from the days of the typewriter. You can google it for more info on the reasons for avoiding double spacing, especially with electronic documents (if you’ve ever seen a double-spaced Word doc converted to a pdf you’ll know what I mean).
Anyway, I don’t want to get into the whole debate here. My interest is the relevant passages from the sixteenth edition of The Chicago Manual of Style—the de facto standard of the publishing industry. No one seems to point anyone to the relevant subsections when the question arises—I can’t find a single on-line source that actually cites the passages.
I’ve had to shorten them for reasons of copyright, but the key bits are quoted (emphasis mine):
2. 9 Word spacing—one space or two?
Like most publishers, Chicago advises leaving a single character space, not two spaces, between sentences and after colons used within a sentence…and this recommendation applies to both the manuscript and the published work.
2.11 Spaces, tabs and hard returns within paragraphs
A well-structured electronic document will never include more than one consecutive character space….
6.7 Punctuation and space—one space or two?
In typeset matter, one space, not two, should be used between two sentences—whether the first ends in a period, a question mark, an exclamation point, or a closing quotation mark or parenthesis.
The MLA says much the same thing. I don’t have the latest edition, so there’s no point citing it.
What often throws people off is the convention set down in the Publication Manual of the American Psychological Association, Sixth Edition. Some people erroneously report that APA specifies double spaces between sentences. Not true. Here’s what it says:
4.01 ….Spacing twice after punctuation marks at the end of a sentence aids readers of draft manuscripts.
The bolded part is essential. APA only recommends it for drafts. The manual itself is single spaced, so are all APA’s publications.
Of course, this rule invites a number of questions—like what the hell is the point of this rule? Think about it: we can all read and understand APA’s single-spaced publications and their manual, but readers of drafts need double spaces? Why? Does our ability to read drastically alter when we read drafts? Is that extra white space necessary for comprehending something that hasn’t been published yet? Seriously, the convention makes no sense.
So do yourself a favour and stick to single spaces unless explicitly directed otherwise.