I think Farhad Manjoo is right about a number of things in this essay, one of them being how strongly and perversely people who insist on placing two spaces after a period before beginning the next sentence continue to cling to this misconception. The need to do so is a rule from the age of typewriters – a rule from the old age of typewriters, as Manjoo points out: typewriters have been working with proportional type from the 70s on, and it is, of course, the existence of proportional type that not only obviates the necessity to use additional white space to indicate the division between sentences, but also means that the old typewriter rule is now plainly wrong. Your wordprocessing client, whichever one you use, and your fonts – except possibly Courier, but why would you be using Courier – are all designed to produce text that is most legible and most pleasing to the eye when there is only one space between a period and the sentence that follows. That is, the rule is only one space after a period.
Am I back? God, I hope so.
Wood Thrush 