No, I'm talking about the space after the period (or ? or !) at the end of a sentence-- one space or two?
I typed my way through endless college papers, my own and my husband's, as well as my MA thesis and I always put two spaces after the period. Just like I learned at my mother's knee (actually, just like I learned in typing class -- back in the Fifties.
So, imagine my surprise when my first manuscript came back to me with enigmatic little red marks all over it, indicating that I was taking up too much space -- that one space after the . or ? or ! was all that I was allowed.
Well, okay, then. I shook my head and tried to unlearn the two space habit of a lifetime, muttering to myself about the inscrutable ways of publishers but never asking why?
Now the mystery is solved! I stumbled upon this article in SLATE (which I visit everyday to read DOONESBURY) and learned that it all has to do with the difference between typewriters (remember them?) and computers.