When the receiver of your text message perceive your typing in all capital as that you are shouting

(CNN) It probably feels like second nature to see a block of all-caps type and assume one of a few things:

• you're being threatened
• you're being yelled at
• you're about to fall head-first into a drunken Facebook rant
• you're receiving some important news
• you're getting a bulletin from the National Weather Service
• (or, maybe all five -- in which case, you're in for a bad day)

The use of capitalization to grab attention, to convey importance or urgency, or emphasize a thought is a common stylistic usage in the internet age. Even the President of the United States seems to be a fan of the practice. On Sunday night, he issued a mostly all-caps Twitter screed directed at Iranian President Hassan Rouhani.

"To Iranian President Rouhani:," he wrote, "NEVER, EVER THREATEN THE UNITED STATES AGAIN OR YOU WILL SUFFER CONSEQUENCES THE LIKES OF WHICH FEW THROUGHOUT HISTORY HAVE EVER SUFFERED BEFORE. WE ARE NO LONGER A COUNTRY THAT WILL STAND FOR YOUR DEMENTED WORDS OF VIOLENCE & DEATH. BE CAUTIOUS!"

The tweet instantly became a meme, with people using his form to mimic all kinds of all-caps phenomena, from a typical scam e-mail forward to shouted Spice Girls lyrics.

While Trump's tweet about the Iranian regime may be riding the line when it comes to typical internet etiquette, he usually favors a more pointed deployment of the all-caps style. In the past, he has used it liberally to emphasize single words or phrases like "ILLEGAL," "GREAT REVIEWS," and of course "FAKE NEWS."

However it is used, whenever you see all caps, you know you should be paying attention -- and possibly covering your ears. But have you ever wondered why?

According to typography expert Paul Luna, it's about taking up space. He told the New Republic in 2014 that "All-capitals provide visibility—maximum size within a given area."

"All-caps in an email looks like shouting because when someone is shouting, you're aware of the shout, and not the nuance," he told the publication.

All-caps isn't an internet-age phenomenon

Believe it or not, the idea of all-caps being seen as something forceful or loud isn't a new development -- there are texts going back as far as the 1800s that make this association.

Dictionary.com credits some early internet message board denizens with setting the modern foundation for what we now collectively understand: Typing in all caps is essentially yelling. And just like yelling in real life, it is sometimes useful, and sometimes just plain rude.

According to Matthew Butterick, the author of "Practical Typography," capitalizing words or even phrases is something that should be done "judiciously." After all, there is a fine line between a deftly-employed shout and a wall of all-caps text that looks like it belongs in an e-mail from your technologically-deficient grandma.

"DON'T CAPITALIZE WHOLE PARAGRAPHS," he writes. "THIS HABIT ORIGINATED WITH LAWYERS AND HAS INFECTED SOCIETY AT LARGE. THUS, MANY WRITERS STILL BELIEVE THAT CAPITALIZATION COMMUNICATES AUTHORITY AND IMPORTANCE."

In addition to being exhausting, all-caps screeds are hard to read. "Cognitive research has suggested the shapes of lowercase letters...create a varied visual contour that helps our brain recognize words," Butterick writes. "Capitalization homogenizes these shapes, leaving a rectangular contour."

This wasn't always the (upper) case

The association of all-caps with big, loud and important stuff is so ingrained in our internet-addled brains, it's easy to forget it wasn't always the (upper) case.

According to Dictionary.com, the Roman script our current Modern English script are based upon didn't even have a lowercase form when they were first used almost 2,000 years ago.

This type of sript is called majuscule, and it basically means by today's conventions, they just yelled everything ALL THE TIME.

Eventually, many scripts evolved to include miniscule, or lowercase letters, and a combination of the two cases was worked out. This combination allowed for emphasis and, because of the varying shape of the letters, an easier reading experience.

While the majuscule case -- or uppercase -- was still deployed to convey what Paul Luna calls "grandeur" or "aesthetic seriousness," the dawn of the internet era has led a lot of institutions to reconsidered their all-caps uses.

In fact, in 2013, the US Navy switched its messaging away from fully uppercase messages. Lowercase messages, it said, "provide a more readable format."

WHEN YOU WRITE IN ALL CAPS IT SOUNDS LIKE YOU’RE SHOUTING.

Using capital letters to indicate strong feeling may be the most famous example of typographical tone of voice. But there are different kinds of strong feelings. Linguist Maria Heath asked a cross section of internet users to rate the difference in emotion between a message in all caps and the same message in standard capitalization. She found that all-cap styling made people judge happy messages as even happier: “IT’S MY BIRTHDAY!!!” feels happier than “It’s my birthday!!!” But it didn’t make sad messages any sadder: “i miss u” is just as pathetic as “I MISS U.” When it came to anger, the results were mixed: Sometimes caps increased the anger rating and sometimes they didn’t, a result which Heath attributed to the difference between “hot” anger (FIGHT ME) and “cold” anger (“fight me”).

A single capped word, on the other hand, is simply EMPHATIC. Looking at examples of all-capped words on Twitter, Heath found that the most common single ones included NOT, ALL, YOU, and SO, as well as advertising words like WIN and FREE: the same kinds of words that are often emphasized in spoken conversations (or commercials). When we want to emphasize something in speech, we often pronounce it louder, faster, or higher in pitch—or all three at once. All caps is a typographic way of conveying the same set of cues.

Emphatic caps feel like the quintessential example of internet tone of voice, and sure enough, they’ve been around since the very early days online. Linguist Ben Zimmer found people in old Usenet groups explaining that all-caps meant yelling as far back as 1984. What’s more intriguing is that capitals were available for emphasis long before the internet as well. The linguist John McWhorter dates shouty caps back to pianist and writer Philippa Schuyler in the 1940s, while author L. M. Montgomery has a character use both capitals and italics for emphasis in her fictional diary entries of the 1920s, which another character criticizes as “Early Victorian”— meaning old-fashionedly melodramatic, even back then. Going yet further back, a newspaper in 1856 described a line of dialog with the phrase “This time he shouted it out in capital letters.”

Back in the heyday of personal letter writing, all-caps was just one part of a broader emotional ecosystem for expressing strong feeling, along with italics, underlining, larger letters, red ink, and other decorative formatting options. The emotional use wasn’t even the most prominent option: All-caps was widely used to avoid the idiosyncrasy of joined handwriting, such as in comic strips, on forms (“Please fill out your name in block capitals”), or in official documents by lawyers, architects, and engineers. Typewriters and early computer terminals made illegible handwriting less of a problem, but they also introduced a new one: They wouldn’t let you type italics and underlines or change font sizes (for that matter, many social media sites still don’t). This created a vacuum into which the preexisting but relatively uncommon shouty caps expanded.

This brings us to a puzzle. Early internet guides like the Jargon File, Wired Style, and website FAQs mentioned all-cap styling, but not to facilitate shouting, the way that *bolding asterisks* or _italicizing underscores_ were recommended to compensate for the lack of other formatting that can indicate emphasis, or a smiley face was recommended to facilitate sarcasm and joking around. No, they were generally trying to discourage it, meaning that a fair percentage of '80s and '90s computer users were writing their routine correspondence in all-caps. (The '90s version of “Oh my god, my boss doesn’t realize that periods are passive-aggressive” was “Oh my god, my boss doesn’t realize that all caps is shouting.”) Where did the idea that it was ever OK to type a full message in block capitals come from? After all, people have been handwriting in lowercase for over a thousand years, and even the melodramatic early Victorians didn’t capitalize everything. Why would anyone suddenly switch to all-caps on a computer?

Part of the blame may go to Morse code, that dashingly dotty system used for sending telegrams. Morse code represents every letter as a combination of dots and dashes, suitable for transmitting as long or short taps along an electrical line: A is dot-dash, B is dash-dot-dot-dot, and the rest of the 26 letters can all be represented as combinations of up to four dots and/or dashes. But if we wanted to include lowercase letters, we’d need a fifth and a sixth dot or dash, because we’d be representing 52 symbols, and telegraph operators would have to memorize twice as many codes. Unsurprisingly, people decided it wasn’t worth it—if all-caps was good enough for the Romans, it would be good enough for telegrams.

Early computers were very similar. Some used teletype machines— the mechanical descendants of telegraph operators—as a way to transmit or print out information. The classic first command that you learn when you start to code is something like PRINT(“HELLO WORLD”), which causes the computer to display HELLO WORLD onscreen. It doesn’t make the computer print out on paper HELLO WORLD, but at one point it did—back before screens, when we commanded computers by keying words into a teletype machine and received their replies printed out onto rolls of paper. Even once computers had screens, storage space was still expensive, as precious as the brain cells of a telegraph operator, so many of them, such as the Apple II, displayed everything in just one case—all caps. Relicts of this setup are still in place on some commercial computer systems: Teletypes are uncommon, but your grocery store receipt, bank statement, or airplane ticket might very well appear from a roll of shiny paper, printed in all-caps.

By the time computers did start supporting lowercase characters, we were faced with two competing standards: One group of people assumed that all caps is just how you write on a computer, while another group insisted that it stood for yelling. Ultimately, the emotional meaning won out. The shift in function happened in parallel with a shift in name: According to the millions of books scanned in Google Books, the terms “all caps” and “all uppercase” started rising sharply in the early 1990s. By contrast, in the earlier part of the century, the preferred terms were “block letters” or “block capitals.” People tended to use “all caps” to talk about the loud kind, while block capitals more often referred to the official kind, on signs and on forms. But the addition of all caps for tone of voice didn’t eliminate the official kind of capitals, which remain common on EXIT signs and CAUTION tape and CHAPTER ONE headings: They may be emphatic, but they aren’t interpreted as especially loud.