Hyphen vs. Dash

Three marks that look similar on a keyboard, do three different jobs, and get treated differently by every title-case style guide.

The marks, and the difference

English text uses three visually similar horizontal marks that are not interchangeable:

• Hyphen (-) — the shortest of the three, joining words into a compound (well-known, self-aware) or breaking a word across a line.
• En-dash (–) — roughly the width of a lowercase "n," used mainly for ranges (pages 10–15, the 2020–2024 term) and some compound modifiers involving multi-word terms.
• Em-dash (—) — roughly the width of a capital "M," used to set off a clause or mark an abrupt break in a sentence — the mark doing the punctuation work in a sentence like this one.

On most keyboards only the hyphen has its own key; the en-dash and em-dash are typically inserted through an editor's autocorrect or a specific keyboard shortcut, which is exactly why they're so often replaced with a plain hyphen in casual typing — and why, conversely, some word processors auto-convert a typed double-hyphen into an em-dash whether or not that was intended.

Why this matters for title case

Title-case rules generally treat a hyphen as joining two words into one compound term, and each style guide has its own rule for whether both halves of that compound get capitalized. AP and MLA capitalize both parts of most hyphenated compounds ("Self-Reliance"); Wikipedia's title-case rule generally lowercases the second part unless it's independently a major word ("Twenty-first," not "Twenty-First"). None of these rules apply the same way to an en-dash or em-dash, since those aren't joining a compound word at all — they're doing sentence-level or range punctuation, a different job entirely.

Why the mix-up causes real problems

Text pasted from a word processor often carries em-dashes and en-dashes that were auto-generated from typed double or triple hyphens. When that text gets run through a case converter, the tool needs to correctly recognize which mark it's looking at — a hyphen inside well-known should be evaluated under the compound-hyphenation rule, while an em-dash setting off a clause should be left alone entirely, since it isn't part of a word.

Where this shows up

Each style guide page on this site documents its specific rule for hyphenated compounds under its "Edge cases we handle" section. If you're cleaning up text that's accumulated the wrong dash characters from a copy-paste, the invisible character finder can normalize smart-quote and dash artifacts back to their plain-ASCII equivalents.

Sources

The Chicago Manual of Style Online and Merriam-Webster — How to Use Em Dashes, En Dashes, and Hyphens.

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