Hence the adoption of the two-space rule-on a typewriter, an extra space after a sentence makes text easier to read. Here's the thing, though: Monospaced fonts went out in the 1970s.

Q: When I took typing 101, I was taught to put two spaces between a period and the beginning of a new sentence. I notice that many students and faculty at the university where I work put only one s… ...

Very few style guides advise using two spaces after a period. The APA, Chicago Manual of Style, AP and US Government Printing Office Style Manual all recommend a single space between sentences.

Hence the adoption of the two-space rule—on a typewriter, an extra space after a sentence makes text easier to read. Here’s the thing, though: Monospaced fonts went out in the 1970s.