As I keep saying and you keep not hearing: this started before the Internet. The Internet had nothing - nothing, nothing, nothing - to do with people stopping the insanely idiotic practice of double-spacing. Double-spacing was for monospaced typewritten output. As soon as that went away, double-spacing went with it. That’s it. Nothing more is needed to explain it.
Single because I grew up on computers instead of typewriters. The first time I learned of the double space rule was in eleventh grade keyboarding class, and I’d been typing for five or more years before then.
The book actually was for computers, but it had us using Word with a monospaced font and actually pressing Enter at the end of lines. It was weirdly anachronistic.
(Note, both of these paragraphs were typed with spaces at the end, as it’s automatic for me.)
Does it have anything to do with typewriters, or is that a red herring? I remember learning about “English spacing” versus “French spacing”, but one look at the list of examples on Wikipedia confirms the long co-existence of a variety of printers’ rules, with no consensus on what looks better. Note that typewriters only showed up in the 19th century, and books aren’t typewritten anyway.
ETA “double spacing” often has to do with vertical white space inserted between lines in a typewritten manuscript. Makes it more legible and provides space for proofreaders’ marks and such. But you should not be typewriting manuscripts these days.
And I’m saying that you’re flat-out wrong. Your facts/assumptions are bad. Simply and completely ahistorical.
Check this out: History of sentence spacing
Here’s the first paragraph:
So as you can see, “double-spacing” came first.
Typewriters (with their monospace text) struck the first significant first blow against double-spacing, because (in an exact reversal to what you say), monospace fonts are the first place where manually putting extra space after a sentence didn’t seem as necessary, because in a fixed-width font a period actually is swimming in a sea of whitespace, making it less necessary to type two spaces to visually emulate an em-space, because a period floating in the middle of a fixed-width space gives you close to a half-space for free. This is in stark contrast to variable-width fonts, which give you nothing for free.
To claim that you need two spaces for fixed width font and only one for variable width font is literally madness. It’s exactly the opposite of what any rational observation of the fonts will lead a rational person to conclude.
As the cite notes, as time passed cheap typesetters making cheap crappy-looking documents with no concern for quality or readability started foregoing em-spaces because paper costs money and more tightly-packed text uses less paper, and thus is cheaper to produce. Also it’s easier to do typesetting when you only have one size of space to worry about. Easier to do = cheaper to to.
And then of course computers came along, and then (more importantly) HTML. Designed by programmers and not typesetters, taking the easy solutions, they wiped out whitespace. Easy peasy lemon squeezy, and now people somehow think low-quality tightly-packed text is right. And are willing to ignore facts, history, and the evidence of their eyes when attempting to defend it.
I don’t mind you preferring bad typesetting - you were raised to it and trained to it, you poor soul you. But please don’t use false history and counterfactual arguments to defend it; it’s tacky,
I guess I have to concede. This board is single spaced and that apparently means you can’t read anything written on it.
My argument was explicitly that typeset spacing **used **to be wider but that - many years ago, before computers - every publisher in existence decided to reduce that spacing.
You also wrote that:
Again, I’ve never said this at any time. My argument is actual history, not whatever flavor you’re using, namely that it was never needed at any time for any good reason. However, it was required for monospaced typewritten documents although not for any other usages in modern history. Other uses never needed it and have ignored it for many decades, most of the past century, in fact.
Sorry to introduce facts. They’re obviously not to your taste. But maybe some of the others reading this will appreciate them.
I think this thread should be moved to Great Debates
A distinct subjunctive form is a quaint old bit of Americana now. I use it sometimes, but it’s dead, as it were. 
I break many of my postings here into single-sentence paragraphs. Sometimes 2 or 3 short sentences. It seems to work well. and posters who post long paragraphs are sometimes chided for not doing so.
Of course, if the board rendered sentences with clear spacing, that wouldn’t be necessary.
FWIW, I automatically double space: I learned on a typewriter, I still use fixed fonts on most of my typing (programming), and all the boards where I post re-render spaces and carriage returns anyway.
The requirement /not/ to use double spacing is, as indicated above, so that the double space doesn’t mess up manual or automatic layout. A smarter layout system would be able to break sentences more clearly, like double spacing does. Perhaps we will get there one day.
You have yet to introduce a true fact that I was not already aware of from another source.
Out of curiosity, in your opinion, why was the extra space required for monospaced typewritten documents?
I literally cannot think of a rational reason why such spaces would be necessary in a (fictional, in your mind only) world where em-spacing and the like have be violently eschewed and panned worldwide in all other forms of printed text.
(Of course in reality the em-spacing and the cheap crappy compressed spacing existed side-by-side for decades. Em-spacing was used in print that wasn’t shitty, like books, and the compressed version was used, well, I’m not actually sure where.)
I’m a technical writer. My job is to create formal documentation. It’s actually in our style guidelines to double space after the end of a sentence.
But I do single space when writing on my phone. Texting, Facebook posts written from my phone, etc. all get a single space between sentences.
… so, both?
I pulled out some old books and some really old books. My grandmother’s copy of Swiss Family Robinson, no date but she put her maiden name in it and she got married in 1904–em spaces for paragraph indent and same space after a period. Skeleton Key to Finnegan’s Wake, 1944–one space that in fact didn’t seem bigger than the other spaces. I’m assuming that was still hot type at the time. But still an em-space for paragraph indents, so the printers still had plenty of them.
But I’m taking issue with whoever said “cheap modern typesetting has only one size of spaces” because if it’s justified, they have to be using more than one size. Like, for instance, for the paragraph indents.
It is interesting, though, that, following the different style sheets I use, for all the NY book publishers it’s one space, but for the Hollywood typescript stuff it’s Courier and two spaces after an end-of-sentence period.
(It is also interesting that I still have to have Word Perfect on my work computer because some manuscripts are still coming in that way. My publisher made me convert my first couple of books to Word, or anyway they strongly recommended it.)
I’d say no, not both, but rather, that this is support for the double space convention.
The first part is what’s relevant. The second part isn’t, B/C AFAIK, FYI, when u txt or write on teh internets u deal w/completely different rules of style. NRN, LOL!
I’ve been saying that the single space approach was cheap when they first instantiated it, which I believe to be true - it was easier than keeping both sizes of indent on hand and also contributed the general compression of text which would, with substantial enough use, save on paper.
Nowadays, of course, it’s only cheap in the sense that it’s ugly. The byte savings you get from omitting that space in a document are negligible to the point of inconsequential; you get no real benefit from omitting it. (Other than complying with an employer’s orders as applicable, of course.)
Also I don’t know that I’ve ever read anything where the paragraph was indented by an em-space. Typically the paragraph indent is bigger that at, at least by a little.
The Wiki history references above appears to blame William Morris (among others) for advocating close-set type and a uniform appearance; presumably he genuinely thought it looked better. And one does, of course, want to avoid rivers of white and similar defects.
As for modern typesetting, it costs the publisher nothing, save for the initial investment of time, to tweak every spacing-related parameter and see what looks better, so in any case it comes down to (good or bad) aesthetic judgement.