One Space After a Period

Early typewriters used monospaced fonts, meaning that the spaces between letters were always the same length, and so, typists started using two spaces to slightly widen the space between sentences. Now that the fonts on your computer are are proportionally spaced, this practice is outdated; it creates unnecessary inconvenience for the writer.

To help guide the reader, it is best to use two spaces after a period ending a sentence in this situation. I would, of course, recommend not using monospaced fonts for body text because it is harder to read than proportional fonts. This paragraph is written using a proportional font. The letters do not line up in columns and each letter takes up the amount of space appropriate to that letter. Using one space after a period at the end of a sentence is appropriate, as the reader can easily distinguish those breaks. Putting two spaces creates a strange gap that is visually unappealing.

Even if you type two spaces after a period on a webpage, the browser will only show one space, unless you force it to display otherwise. In order to force whitespace to display you need to either use the non-breaking space to add single spaces, the <br> tag to add line-breaks, or the whitespace property in CSS to change how whitespace is handled on the page.

I had a conversation with Robert Frost (Flight Operations Directorate at NASA, trains astronauts for the ISS, pretty cool guy) about his usage of two spaced after a period, and he told me that “civilized people still use two spaces because it makes it easier to see where sentences begin and end.” Fair point.

Definite conclusion: The typist may wish to continue using two spaces after a period, but the typographer should not.