Hyphen vs Dash

The hyphen (-) is the shortest of the marks and the only one on a standard keyboard. Its job is to bind parts of a word or phrase into a unit:

• Compound adjectives: a well-known author, a five-year plan, an eight-hour flight.
• Compound nouns: mother-in-law, editor-in-chief, runner-up.
• Prefixes before a capital or a repeated vowel: re-enter, pre-existing, anti-inflammatory (conventions vary).
• Numbers: twenty-one, thirty-five.
• Line breaks: a hyphen at the end of a line shows that a word continues on the next line.

Style guides differ on how much hyphenation compounds need. A compound adjective before a noun is usually hyphenated (a well-known author), while the same words after the noun often are not (the author is well known). The mark itself never changes; only the convention does.

The en dash (–) is longer than a hyphen. It marks a span or a relationship between two things rather than joining them into one word:

• Ranges: 2019–2024, pages 10–24, Monday–Friday.
• Scores: 3–1, 21–17.
• Connections: the London–Paris route, a north–south axis.
• Open compounds: a New York–based writer, a Nobel Prize–winning team.

The en dash is not a hyphen with extra space. Replacing the hyphen in “well–known” with an en dash is a typographic error, because the two words are being joined, not spanned.

The em dash (—) is the longest common dash. It breaks the flow of a sentence to add an aside, an explanation or an interruption:

• The plan — which nobody had read — was approved.
• She opened the door — and stopped.
• There was only one option — wait.

An em dash is stronger than a comma and less formal than parentheses. It can usually be replaced by one of them, so use it when you want the pause to be felt. Spacing follows the style guide: closed up in many book styles, spaced in some news styles.

The minus sign (−, U+2212) is a mathematical operator, not punctuation. It is wider and more centred than a hyphen and matches the plus sign in an equation: 12 − 5 = 7. A negative number uses the same character: −5, not -5, in typeset mathematics.

In plain text, people type the hyphen for both jobs. That is understandable, but it is not the same character, and in a document that mixes prose and formulas the difference is visible.

1. Is the mark joining parts of one word or phrase? Use a hyphen: well-known, mother-in-law, twenty-one.
2. Is it spanning two endpoints or connecting two equal terms? Use an en dash: 2019–2024, London–Paris.
3. Is it interrupting the sentence or setting off an aside? Use an em dash: the plan — still unfinished — was approved.
4. Is it arithmetic or a negative value? Use a minus sign: 12 − 5, −0.5.

If you are working in plain text with no dash available, a spaced hyphen is a common fallback for an aside, and a hyphen between numbers is common for ranges. The result is readable, but it is a compromise, not the typographic ideal.