The average American swears 80 to 90 times a day. There are no studies about how often the average politician swears, but anecdotal evidence argues for a lot. Beto O’Rourke has entered a “f--- it”phase as journalist Michael Kruse puts it, dropping the profanity as often as he breaks into high school Spanish. Joe Biden called the signing of the Affordable Health Care Act a “big f------ deal” in 2010 and has responded to reporters’ questions with “Who gives a s---?” Julián Castro and Kamala Harris like to refer to things they disagree with as “bulls---;” Tulsi Gabbard accused President Donald Trump of “being Saudi Arabia’s b----.”

While considered taboo, swearwords shouldn’t necessarily be excised from personal or even public discourse.

Trump himself is a famous swearer, having used a vulgarity to address the Chinese, arguing that the best way to deal with the Islamic State militant group was to “bomb the s--- out of them” and, of course, revealed his fool-proof strategy for seducing women: “Grab ’em by the pussy.” Given all the curses flying, why should anyone be surprised or bothered that Trump called the Democrats’ investigations into him “BULLS---” on Twitter?

Swearwords have a power in excess of their literal meaning. These words change over time and among different social groups — while we probably all agree about the F-word, some of us might not put some of the others mentioned above in this category. But whichever words we deem obscene, they serve important purposes in our culture. A word like “f---”“kidnaps our attention and forces us to consider its unpleasant connotations,” according to the linguist Steven Pinker.

While considered taboo, swearwords shouldn’t necessarily be excised from personal or even public discourse. There is, however, a reason that they have historically been avoided by presidents, and there are negative consequences to their frequent utterance by Trump: They are part and parcel of norms and values in government that we are seeing eroded across the board. Swearing can be fun, appropriate and creative under the right circumstances. When done publicly and constantly at the highest levels of government, though, it is a sign that something is seriously wrong.

To understand how this works, let’s first consider more generally what swearwords dofor anyone who uses them — including politicians. Swearwords are not like most other words. They are stored and processed differently in our brains, having a close connection to the limbic system that controls emotions such as fear and aggression and generates our fight-or-flight response.

When we hear people swear, we interpret these words as coming straight from the heart, representing the “truth” about their feelings. Studies have shown that we often associate swearing with the truth, full stop. We are more likely to believe the testimony of a witness who says something like, “I f-----’ saw him!” for example, than one who states the same thing without the obscenity. In Trump’s case, the potential advantages of this are clear. He said the investigations were “BULLS---” (in all caps), ergo he must be telling the truth.

People are also more likely to remember swearwords. Psychologist Timothy Jay has done word recall tests in which he gives participants a list of 36 words then later asks them to write down all the ones they remember. People nearly always put the N-word and b----at the top of the list, while forgetting even strongly charged words such as love and anger. Trump’s “BULLS---” will stick in the mind — and sound much more genuine — than if he had tweeted that the Democrats’ investigations were, say, “unwarranted, gratuitous and unconscionable.”

Finally, swearwords are often seen as, and to some extent are, the language of the “regular people” nearly all politicians seek to appeal to. Statistics show that members of the working class swear the most and employ the most obscene terms. For many Americans, too, cursing still has associations with masculinity— a person who swears is someone who tells it like it is, and damn the consequences. If you’re aiming to be a candidate voters “want to have a beer with,” you’ve got to speak their lingo, and that’s often profane.

Trump is a master at deploying swearwords for all these purposes, and has been doing it for years. The problem with his Wednesday tweet, then, is not actually his particular word choice but its context. It has to do with a linguistic and cultural ideal conveyed in all speech but rarely considered: decorum.

If you had to define decorum, you might describe it as an exaggerated, old-fashioned politeness, the kind of “proper” behavior you’d have to exhibit when eating dinner at your grandmother’s house. But decorum is both simpler and more powerful: It is the idea that certain kinds of language, and therefore behavior, are appropriate for certain situations.

At your grandmother’s table, that familiar sense of decorum does indeed apply. There, you behave with propriety, keeping your elbows off the table, perhaps answering her questions with “yes, ma’am” and not going into detail about your latest hookup. But at a dive bar, decorum demands different language and behavior — here you drink to excess, stumble into strangers and yell “I f-----’ love you guys!” to your buddies at the end of the night. Decorum is being observed in both these situations, since the language and behavior is appropriate to each.

What are the rules of decorum for a president’s Twitter feed, though? We have previously set high standards for the public speech of presidents, whatever they have gotten up to in private. When linguists want to find examples of formal American speech, they turn to White House press briefings (or at least they used to, when there were press briefings). These sessions were thought to feature Americans’ most elevated diction, our most correct grammar. If you were looking for people using “whom,” you’d go to the White House, even before you’d check out how the professors were speaking at university faculty meetings.

Swearing is not part of such high-register speech, so when politicians, even Trump, swear, they tend to do it orally and in quite informal circumstances. O’Rourke may say “f---” dozens of times at rallies or in interviews, but, should he be elected president, he’d be unlikely to write it down in a bill or utter it at an official appearance with another head of state. Trump has said “bulls---” dozens of times in semi-private and it isn’t a big deal, but Twitter is a public forum where many expect stricter presidential standards of decorum to apply.

On the other hand, we are talking about Twitter. People swear there even more than in “real life” —one in 13 words on Twitter is a swearword, usually a form of f---. Bulls--- is totally appropriate — mild, really — when considered in the general context of other tweets.

Most people assume that the decorum of the White House should outrank the decorum of Twitter, but Trump has tried to thread the needle. This indicates that he, too, pays deference to these unwritten rules on some level, even as he pushes their boundaries. He tweeted “BULLS---” from his private account, @realDonaldTrump, not from @POTUS, his official presidential one. He often retweets himself, but not this time.

On some level he seems to want to preserve the high linguistic standards of the presidency, just as when he couldn’t bring himself to say “jock strap” in a press conference with the Finnish president, making do with insulting House Intelligence Committee Chairman Adam Schiff by scoffing, “He couldn’t carry his ‘blank’ strap,” referring to Secretary of State Mike Pompeo. Yet Trump also wants to keep participating in the coarse idiom of Twitter, which helped him win the 2016 election and shores up support among his base every day.

Most people assume that the decorum of the White House should outrank the decorum of Twitter, but Trump has tried to thread the needle.

Decorum, however, doesn’t just stipulate what types of language are appropriate for which types of situations: It is actually a fundamental part of a functioning government. We are discovering every day that what we took for granted as firm procedural rules or bedrock legal principles are actually just the gossamer guidance of decorum.

If a president doesn’t want to release his tax returns, stop inviting foreign leaders to put money in his pockets by staying at his hotels or make sure that government agencies are staffed properly, no one can make him, apparently, if his base approves.

These unwritten standards are in flux, but they haven’t been entirely dispensed with yet. Breaking them can still shock, as Trump’s “BULLS---” tweet shows. As it happens, Elizabeth Warren’s favorite “bad word” is “poop.” I’d say this bodes either very ill, or very well, for her campaign.