President Donald Trump boasted Tuesday on Twitter about his ability to write. Specifically, he defended his seemingly random use of capitalization. His method?

He said he uppercases certain words for “emphasis” — not because they should be capitalized.

The president’s original tweet about capitalization: “After having written many best selling books, and somewhat priding myself on my ability to write, it should be noted that the Fake News constantly likes to pour over my tweets looking for a mistake. I capitalize certain words only for emphasis, not b/c they should be capitalized!”

(That tweet, which was later deleted and reposted, also used an incorrect homophone — “pour” instead of “pore” — and contained a dangling modifier. But that’s a story for another day.)

Trump’s distinctive philosophy of capitalization has brought us Witch Hunt and Fake News, a big-B Border and Crime with a capital C.

But what are the actual rules of capitalization? And, in an era of tweeting, texting and Trump, when is it OK to break them? Here’s a handy guide.

Why are we talking about capitalization? Experts say overcapitalization can be traced to the 17th and 18th centuries, when it was common to uppercase significant words. In line with the times, the Founding Fathers used this style in the U.S. Constitution, said Kory Stamper, a lexicographer and the author of “Word by Word: The Secret Life of Dictionaries.” Over the past several years, Stamper said, she has noticed that some people with conservative viewpoints have increasingly used frequent capitalization. “There is definitely a heavy tie to wanting to mimic the Founding Fathers, and they seem to have latched on to capitalization as the way to do it,” she said.

When should I use capitalization? Most people know that you should capitalize the first word in a sentence, the pronoun “I” and proper nouns. There are other times when capitalization is needed, but, even at this basic level, things can start to get tricky. “The confusion tends to be around what’s considered a proper noun and what’s not,” Stamper said. “Is ‘earth’ a proper noun? When do you capitalize titles and honorifics like ‘president’ or ‘prime minister’?”

Is it kosher to capitalize for emphasis? It depends, said Bryan A. Garner, a grammarian who is the author of “Garner’s Modern English Usage.” Some acclaimed writers, such as David Foster Wallace, have used capitalization for emphasis in a way that many consider literary, he said. But, he said, the rules are there for a reason — you have to know them in order to break them. So if not capitalization, then what? Use italics, Garner said. If you are tweeting or texting, he said, you can use asterisks on either side of the word for *emphasis*.