For example
"Put that down!" he shouted.
versus
"PUT THAT DOWN!"
I noticed Fitzgerald used the former to convey shouting in The Great Gatsby, and was wondering if this was just a stylistic choice or capital words just didn't have that meaning in his time. The technique is viewed as an eyesore among some, but is definitely used, especially in casual writing.
So, when did capitalizing words in dialogue mean the speaker was shouting? When did people begin to associate capitalized letters with emphasis?
All-caps indicated emphasis for centuries, and were occasionally used to indicate shouting as far back as the 1940's (as evidenced in Philippa Schuyler's biography).
The practice became widespread in Usenet newsgroups around 1984, when one user summed it up as:
there seem to be some conventions developing in the use of various emphasizers. There are three kinds of emphasis in use, in order of popularity:
and
if it's in caps i'm trying to YELL!
The source is the New Republic, but they cite their contributing editor John McWhorter who's a well known linguist.