It's truly unbelievable that so much has been written on this topic. And, here I am, writing more!
This is a debate that has raged on, sometimes viciously. All of it over a teeny, tiny space. Hundreds of them. No, millions!
The truth is, although PCs have changed the approach, some people still staunchly choose to use two spaces, such as those who work in the legal profession. The only right or wrong here depends on style. If the organization for which you work uses a style guide, consult that. If the university or department for whom you are writing a thesis provides a style guide, that's your go-to place. I most often use APA, but I have edited in APA for a university that preferred two spaces. The uni trumped APA.
From my perspective, "one space" is much easier and more practical. Here's the reason why:
If two spaces are required, then the editor or proofer must go through the entire paper carefully to ensure two spaces are used. If one space is required, the Find/Replace feature simply replaces two spaces with one.
Find/Replace can't be done from one space to two because the result will be two spaces after Dr., Mrs., St., U.S., and so on.
Here's an interesting article about spacing after end marks.
(p.s. I "borrowed" this image from BKA Content.)
Meet the Editor
I'm Coreen, and I am a copy editor, writer, instructor, digital marketer, and student of PR and Communications for organizations doing positive work in the world.