The anecdote I heard was that the extra space made it more clear when sentences were ending based on how the fixed-width typeface would read. With proportional fonts the spacing is already clear enough with 1 space, and that has become the conventional thing. So adding the extra space creates too much space now. It certainly sends a signal to me that the person has absorbed a “rule”, but not its purpose, which I think doesn’t reflect well on that person. But on the whole that’s a minor side note and I try to not go overboard interpreting details like that.

> With proportional fonts the spacing is already clear enough with 1 space.

That's your opinion, and a bizarre one at that, since one-space isn't any more clear in a proportional font than a non-proportional font. Proportional fonts help pack letters within a word, not pack words within/between sentences.

> It certainly sends a signal to me that the person has absorbed a “rule”, but not its purpose,

It sends a signal to me that a person looks for bizarre ways to feel superior to others, instead of trying to understand why someone behaves differently.

> Proportional fonts help pack letters within a word, not pack words within/between sentences.

I was probably wrong to try and fuzzily remember an anecdote rather than look it up :) but my understanding was that in a proportional font the combination of a period and space was good enough to show the end of the sentence clearly for whatever reason.

> It sends a signal to me that a person looks for bizarre ways to feel superior to others, instead of trying to understand why someone behaves differently.

This is fair. Though I promise I don’t feel superior to pretty much anybody if that helps. Learning about this actually came from wondering why some people used two spaces after sentences, not starting out judgmental. I think I was mainly thinking of formal contexts where you would already be judging somebody's choices (resume, professional portfolio, publications) more so than just random language use in comments or whatever. But I didn't put my finger on that last night!

I had this uneasiness writing my own comment and reading your comment, and did some actual reading this morning, and this turns out to be one of those things where the story I absorbed about it was too simple. There seems to be ongoing debate about this just like everything else, and even though most publishers and editors prefer 1 space after a sentence. I had though I heard that spaces after periods actually render a little wider anyway but that seems to be wrong?

I knew I worded my comment kind of badly and probably shouldn’t have made it in the first place. But at lest posting it helped me get corrected on my assumptions.

Except the fact that the two spaces before a period far predate the typewriter.

Wider sentence spacing certainly predates the typewriter, but the question then was not "how many spaces" but "how much space".

Someone writing by hand obviously does not count a discrete number of spaces, and a cold-metal typesetter has a wide variety of spaces available: they might use a one-and-a-half-en space (either a single piece of type or an en space followed by a half-en space) or an em space.

It must have been the introduction of the typewriter that brought the idea of "two spaces" instead of "wider space".

> It must have been the introduction of the typewriter that brought the idea of "two spaces" instead of "wider space".

Come to think about it, why not the movable type printing press as the starting point?

(please ignore this, I apparently didn't read your comment fully!)

You only used one space in this comment ;)

I wonder if that gets changed by the site or something. I remember thinking "I better be sure to use two spaces otherwise someone will call me out on it."

Here's a test. I definitely put two spaces prior to this sentence.

EDIT - indeed it seems that HN changes the spacing.

Check the source.