How widely used is the "two-space-sentence-ending" convention?

Question

I was reading a manual discussing about how a sentence should be properly ended by convention. Here I quote:

you follow the American typist's convention of putting two spaces at the end of a sentence. That is, a sentence ends wherever there is a ‘.’, ‘?’ or ‘!’ followed by the end of a line or two spaces, with any number of ‘)’, ‘]’, ‘'’, or ‘"’ characters allowed in between.

-Reference

I was not in American area and I study English as a second language. I have never heard about such convention before. Therefore I am a bit curious of how widely this convention is used.

Since the mentioned section of this manual was discussing about human language. It seems relevant to ask here.

Answer 1

As Peter Shor indicates in a comment, the "two spaces after end punctuation" rule is a relic from the days of monofont typewriters: To help readers of text set in such type recognize sentence breaks more easily—and perhaps to give the finished page a bit of visual variety in a layout constrained by monofont uniformity—some style guides in those days recommended adding a second space after each sentence in each paragraph.

I first encountered this style guideline at the student newspaper for the very small college I attended in the 1970s. We typed all of the text for it on manual Olympia typewriters that seemed to be made of cast iron and looked as though they had survived battlefield use during World War II.

My last and most horrific brush with the rule came in 1996 at a fairly fancy startup magazine that used Quark (at the time the most sophisticated publishing software available). Our designer had set up all of the specifications for font type, font size, letter spacing, etc., and the higher-ups had approved them all. But on the last weekend before the first issue went to press, our CEO showed up, examined the page proofs, and decided that the text looked too cramped. His solution: Add another letter space at the end of each sentence—just as if we were working in monofont.

Since our magazine was full of abbreviations that ended in periods, we couldn't just run a universal search-and-replace using ". [+ one space]" and ". [+ two spaces]"; instead, I had to go through the entire issue, adding a second letter space after each sentence. It took hours.

As far as I know, that magazine in 1996 was the last commercial consumer publication in the United States to enforce the two-space rule. I certainly hope so.

Answer 2

Just for the record on this nice and historic question, I will go ahead and say that:

In the (today extremely unusual) circumstance that you are using a monospaced fount, I'd suggest really it is probably better to continue with the two space rule.

Recalling that, the very reason for the two-space approach is/was simply for clarity:

Examples could include:

(1) You're an art director, and you're making a poster that features a sentence fragment in "old-fashioned broken typewriter look" (so, it's a "crime novel look"). In this case you should do it because, well, that's how typewritten pages look.

(2) In the very unusual circumstance of writing computer code. The comments (ie, English human-language sentences in the code) are, indeed, in monospaced fount. FWIW I'd point out that, thus, it's better to use the double-space in such writing. (Indeed, this is a good example where clarity is everything.) for example FWIW I do this and all employees have to. It would be difficult to say if this is "common with programmers over 30" but anyone who's used to typing monospaced, this would be the only (I can think of) present situation where it still happens.

Example!

You could click to say github to find swathes of example computer code in various computer languages.

(An interesting aside there is that conventions like capitals appear to have fallen by the wayside, but the double-space remains a good sentence clarifier.)

Note - perhaps someone else can think of another example where, today, one actually writes in monospace. Even text-messages, say, are now flawlessly typography'ed.

(3) If you are - say - a spy, or in general, for some reason you are writing a message on a monospaced system (so, you're a spy sneaking a message out using an old typewriter), I encourage you to use the double-spacing, again simply for clarity and decisiveness - you don't want a comma even possibly confused with a point. (I guess in old-fashioned telegrams using "STOP" is the extreme way to clarify sentences.)

Finally I point out that when handwriting with a pen or pencil - of course, extremely few people now handwrite multi-sentence messages for any reason - I observe that it is common (english speakers, writing) to leave a fairly substantial gap between sentences, much bigger than the word gap. So, there's kind of an analogy.

(On that note the only human being I have heard of who handwrites today, is the popular author Neal Stephenson who apparently writes by hand when writing a ms. one could sift through his paper ms and see if he leaves a bigger gap!) Thanks for the great question!