Despite whatever you’ve been told in the past, you should only put one space after a period, not two.
Is this arbitrary? Sure it is. But so are a lot of our conventions for writing. It’s arbitrary that we write shop instead of shoppe, or phone instead of fone, or that we use ! to emphasize a sentence rather than %. We adopted these standards because practitioners of publishingâ€”writers, editors, typographers, and othersâ€”settled on them after decades of experience. Among their rules was that we should use one space after a period instead of twoâ€”so that’s how we should do it.
In my high-school typing class, we were working on ancient ICON computers which used monospace type, and were told to leave two spaces after a period for readability. I then spent years developing muscle-memory that had me double-tapping the spacebar after every full-stop. In university, I started writing for one of the newspapers and got yelled at for putting in double spaces and messing up the copy-setting — I learned quick. Fast-forward to book design, and given any sort of manuscript, getting rid of the double spaces is one of the first priorities. Remember, just one space.