I worked in publishing after finishing university before deciding that I wanted to be a lawyer and working in a law firm was the way forward (it' s not, BTW). I'm showing my age but this was in 2000, the beginning of electronic publishing and use of SGML (Standard Generalised Mark-up Language) to format text. Put somewhat simplistically, SGML means that the same copy can be used for physical printing and web publishing. Publishing houses have very strict style guides and a lot of inflexible rules on things like spacing, and this is when I first learnt that you should only insert one space after a full stop.
Back in the olden days when typewriters were in use, all characters were monospaced - ie. the typewriter allocated as much space to place (say) an "m" as for an "i". Monospaced type makes text look messy and uneven and it can be difficult to spot spaces between sentences. For this reason typists added a double space following a full stop.
Since computer type-setting came into general use (according to the article sometime in the mid-1970s), proportional fonts have meant that this extra space is not necessary. More than this, "typographers", those international guardians of what is write* in typesetting have decreed that TWO SPACES AFTER A FULL STOP IS WRONG. Publishing houses (and Universities, and smart people) do what experts in a field say.
I left to become a lawyer because while this was all very interesting the pay was rubbish and coding in SGML and having arguments with nerds about typography felt like a waste of a borderline LLB degree. In my first legal job I used to correct my secretary and ask her not to insert two spaces after a full stop. She complained to the office manager and I got a telling off. I knew I was right but didn't have any evidence, and I wish I'd had this Slate article back then. Not that I'm bitter, but in the end we'd all rather be proven right than wrong, wouldn't we?
Here endeth the lesson.
* See what I did there?
