Field guide / Rule 02 — Dashes
Your keyboard has one horizontal stroke; typography has three, and they are not interchangeable. One joins words, one spans a range, one breaks a sentence — and the difference between them is one of the quietest marks of a set page.
The typewriter had a single dash key, and the computer kept it — so the hyphen (-) is the only one your keyboard sends. Real typography draws three marks of increasing length, and each has one job:
The hyphen joins: well-known, state-of-the-art, a twelve-page brief. The en dash — the width of a capital N — spans a range or a relation: pages 3–5, 1998–2003, the London–Paris line. The em dash — the width of a capital M — breaks a sentence to set a phrase apart, the way this one does.
The one confusion worth clearing up is the en dash, because most people reach for a hyphen where it belongs. Any span you could read as “to” or “through” takes an en dash: Monday–Friday, 10–20 mg, the 2019–2024 term. So does a relation between two equals — a score of 3–1, an author–publisher agreement.
The em dash is the one people reach for too much — it is a strong break, so a page peppered with them reads as breathless. Used sparingly it earns its weight. And note the spacing: an em dash is set flush against its words by default. Only if it looks crushed — particularly on screen — is it fine to add a single space on either side.
You do not need the special characters. Type the plain-ASCII shorthand — two hyphens for an en dash, three for an em dash — and we set the real mark on the way out. A single hyphen we leave exactly as it is, because a lone - is almost always a genuine hyphen, and guessing a range from one would break more than it fixed.
A single hyphen joins words — left untouched, always.
Two hyphens become an en dash — the mark for a range.
A span of years reads as through — an en dash, not a hyphen.
Three hyphens become an em dash — the sentence break.
In short
Three marks: the hyphen joins, the en dash ranges, the em dash breaks. Type -- and --- and we set the real dashes for you — and we keep our hands off every lone hyphen, because that one is usually right already.
Want to see it on your own text? Convert a document and read the cleanup report — every dash we set is counted there.