Most computer keyboards have a character key that produces this symbol: -. This is a hyphen, used to join compound modifiers, compound numbers (fifty-seven) and for certain nouns (father-in-law, break-in). The mark’s proper use is quite fiddly: we say “well-heeled benefactor” but remove the hyphen for “benefactor is well heeled” and omit it if the first word of the modifier ends with -ly (“absurdly wealthy benefactor”). For compound nouns, the hyphen is often a transitional phase from two words to one: old books contain the compound noun “to-morrow” and even older ones use “to morrow”. It is very commonly omitted in casual or informal writing.

Computer keyboards, for the most part, cannot directly produce this symbol: –. This is a dash, more specifically an en dash. It is used in Commonwealth countries to denote the dash punctuation mark – that versatile sentence splitter that can perform the function of a comma, colon or semicolon with a bit of additional drama.

In the United States (and Oxford University), this punctuation mark is more commonly represented with a slightly longer line: —, the em dash, usually typeset without surrounding spaces.¹ As with its shorter brother, you will not find an em dash on most computer keyboards.

Because a spaced en dash is used for the same function as an unspaced em dash, the sentences below are semantically identical:

• The entire project – which involved complex programming and late nights – was finally completed on schedule.
• The entire project—which involved complex programming and late nights—was finally completed on schedule.

But most online articles about the difference between these three marks give a US-centric explanation that omits any mention of the spaced en dash. If you ignore it, you get to live in a simple world where unspaced hyphens are used to join words, unspaced en dashes denote ranges (1–10, December 2025–January 2026) and unspaced em dashes join clauses and phrases. Unfortunately, that world is imaginary, and real differences in typographical conventions mean that the terms “em dash” and “en dash” cannot be used to refer unambiguously to the dash punctuation mark – we must make a distinction here between the punctuation mark (dash) and its differing presentations (optionally spaced em dash versus spaced en dash).

The affordances of computer keyboards mean that in much informal writing, a spaced hyphen is used to signify the dash - like so. Even if computer keyboards did have two extra keys for slightly longer lines, most people would probably still not concern themselves with the distinction. If you weren’t previously aware of it, I apologise for cursing you with this knowledge.

Someone who knows not to use hyphens instead of dashes but for whatever reason cannot input the correct symbol will use a double hyphen to denote a dash ‐‐ like this (Commonwealth)‐‐or like this (US). But most people conscientious enough to do this will keep it for their rough drafts and dutifully convert the hyphens to dashes prior to publication. On the other hand, if you’re using a spaced hyphen, it’s because you meant to use a spaced en dash, consciously or unconsciously.²

Between the affordances of computer keyboards and the almost total abandonment of the em dash outside of the US, there may have been a time when the em dash was poised to fall entirely by the wayside, like the manicule before it.

The em dash is the nineteenth-century standard, still prescribed in many editorial style books, but the em dash is too long for use with the best text faces. Like the oversized space between sentences, it belongs to the padded and corseted aesthetic of Victorian typography.

Robert Bringhurst, The Elements of Typographic Style

The em dash puts a nice pause in the text—and it is underused in professional writing.

Matthew Butterick, Practical Typography

But clearly there were enough em dashes in print and Internet writing for the mark to be thoroughly imprinted on modern LLMs. Both of the above quotes predate the November 2022 release of ChatGPT and the accompanying explosion of unspaced em dash usage.³ The proliferation of AI text has gotten more people than ever before to notice this typographic element, and it is now commonly derided as the “ChatGPT hyphen”. The presence of em dashes is now the one of the simplest, at-a-glance heuristics one can use when investigating whether a given piece of text was generated by an LLM.⁴ It’s not foolproof, but if someone you know switched from spaced hyphens to unspaced em dashes sometime after ChatGPT’s initial release, it’s pretty likely that an LLM was involved somewhere along the line – especially if that someone is not American.⁵

My heart is with all of the pedantic punctuators who have spent years going out of their way to type Alt 0151 or Ctrl-Shift-U 2014 or especially Ctrl-Shift-K M- and are now being accused of outsourcing their writing to an LLM as a result. It’s unfair and my preference for the Commonwealth convention is the only thing that’s saved me from a similar fate.

ChatGPT’s love of the em dash has also greatly softened my previous annoyance at spaced hyphens. The use of a spaced hyphen rather than a dash now serves as a pretty solid indicator of humanity, much like typos and comma splices. But we should be wary of leaning into this, lest “doing things properly” become an AI tell.