In his first language video in four years, the linguistically educated Tom Scott explains how the rise of digital communication has changed grammatical standards and norms, particularly in the case of punctuation and capitalization. Scott notes how audible inflections and intentions are largely absent, so capital letters and specific punctuation marks denote different meanings in the online arena.
In standard written English, capital letters don’t convey much actual information. They just show proper nouns and the beginning of sentences. And while that might make a paragraph easier to read, we don’t flag those up at all when we speak, it’s not necessary. So in informal conversations, those that feel like speaking, we don’t need capital letters. But that means online communities could use capitals to convey something else that does appear in conversation: tone. So all-caps became shouting.