carriage returnsOnly when you want a new paragraph
On manual typewriters, the carriage was the part on top that held the paper and scooted leftward as you typed. At the end of each line, you’d push a lever to move the carriage to the beginning of the next line. On electric typewriters, this lever became the carriage return key, which you’d press at the end of each line.
The terminology has stayed with us, but on a word processor, you only use a carriage return to start a new paragraph. (In HTML, you use a formatting tag to denote a paragraph—a carriage return has no visible effect.)
<p> … </p>
As with the word space, use only one carriage return at a time. It’s common to see multiple carriage returns used to add vertical space between paragraphs. Bad idea. If you want vertical space after a paragraph, use space between paragraphs.
“But it’s so much easier to type two carriage returns.” I know. But in long, structured documents, extra carriage returns create unpredictable consequences as the document is edited. Whatever time you save with the shortcut will cost you later.
What if you get a document that’s already littered with double carriage returns? Search-and-replace works with white-space characterstoo.
How to replace double carriage returns
WordFind and Replace → Replace → More. Use the Special menu to put two Paragraph Marks in the Find what box, and one Paragraph Mark in the Replace with box. (Careful: you don’t want the Paragraph Character, which denotes the literal ¶ symbol.) Click Replace All.
Mac OS WordEdit → Find → Advanced Find and Replace → Replace → click triangle-shaped box in lower left to reveal the Special menu, and then continue as described above.
PagesOpen the Find panel (either Edit → Find → Find... or ⌘ + f). In the first box, type \n\n, and in the second, type \n. (\n is a special code representing one carriage return; \n\n represents two.) Click the right-pointing arrow in the lower right of the Find panel. Click Replace All.
by the way
A common nonsense objection to one space between sentences is “muscle memory”: roughly, I learned to type on a typewriter using two spaces, and my habit is too strong to change. Of course, these same people successfully changed their habit of typing a carriage return after each line, as typewriters required, to only typing one after a paragraph. Whatever.