ChatGPT、Claude 等 AI 为何爱用破折号（em dash）？它是什么、该怎么用？

以下是视频口播的自动转写，可能有错字。

Why does ai love m dashes? What is an m dash? What are they for? How do you use them? Let me explain everything you need to know about m dashes.

So these long dashes in the middle of sentences have become the most obvious sign that someone used ai. And that's because large language models like ChatGPT were trained on vast amounts of human writing and they learned how to write properly.

But once you've trained a large language model, it's really hard for it to make exceptions. So that's why even if you put don't use m dashes in your instructions, You will still see it use m dashes sometimes, so we're just going to have to embrace the m dash.

And anyway, they're really useful. So I'm going to tell you how to use them properly in a sec. But firstly, why is it called an m dash?

Well, an m is a unit of measurement that we still use today with fonts on websites and documents, but it originates from print impressors and the people who did the typesetting on those printing blocks, placing all the little metal stamps that stamped the characters onto a newspaper or book page.

Well, sometimes they needed to create spaces on the page, and so they had different sizes of blank spacer blocks, and one of them was called an m quadrat.

And that one was always square, it was equal width and height. Its actual size varied, but it was determined by the typeface that it was within.

So whatever height that typeface was, would also be the width of the m quadrat. And that's why the m dash looks pretty long, because if you turned it around, it would be as tall as the tallest, biggest character in that typeface.

So now you know that in typography, 1 m is 1 times the height of that typeface. In previous centuries, m dashes were used a lot, particularly in the 18th century, to the point where there was actually a backlash against them.

So this is not the m dashes first rodeo as a vilified punctuation mark. In 1795, a language expert called lindley murray warned about their misuse by hasty and incoherent writers.

But they are useful and they are different from the other dashes. There are actually three ways to use an m dash. The first is to contain an aside.

I left my phone, which was an iphone 18, in the cafe. Today, people would often use commas or brackets for that, but the dashes give it more emphasis.

In fact, some people do call the m dash an emphasis dash, but that's not actually where the name comes from, as we've just learned.

Secondly, an m dash could tee up an explanation or a punchline to a sentence. So, i've forgotten one thing, my phone. Now, a colon would work there fine as well, but the dash just gives you a more abrupt reveal.

And then thirdly, it can show speech being cut off abruptly mid-sentence. How about we, and someone cuts in. You often see this in scripts or dialogue in novels, where someone's unexpectedly interrupted by another person or something happening.

So that's how to use an m dash, but it's just one of three dashes that we commonly use in english, because we also have the hyphen.

And the end dash a hyphen is the short one that joins words together like well known and end dash is a little bit longer and that often means two.

So like pages 10 to 20 and then an m dash as we've talked about that's the longest one. It's for those breaks interruptions or points of emphasis and if you want to type one on a mac, it's shift option hyphen or on a windows, you hold down alt and type 0151.