1 The rule in plain terms
The em dash is the long dash that signals a break in thought, an aside, or an abrupt change in a sentence. In AP style, it is set closed up—no space on either side. Think of it as a stronger version of a comma or parenthesis, one that pulls the reader up short. The en dash is shorter, about the width of a lowercase n, and it has two main jobs: it shows a range (as in dates, times, or numbers) and it links compounds when one part is already hyphenated or made of multiple words. For example, a range of years takes an en dash: 2019–2020. A compound like pre–Civil War takes an en dash because Civil War is two words. The hyphen, the shortest of the three, joins words into a single concept, as in a well-known author. Writers often blur these marks, but the distinctions are not arbitrary. Each dash has a specific role, and using the right one helps readers parse relationships quickly. When you are unsure, ask what the dash is doing: breaking a thought (em), spanning a range (en), or gluing words together (hyphen). That question will steer you to the correct mark.
2 Why editors enforce it
Editors enforce dash distinctions because they affect clarity and credibility. A misplaced dash can make a sentence ambiguous or even nonsensical. Consider a range written with a hyphen: 2019-2020. It looks like a compound adjective, not a span of time. Readers may stumble, wondering if it means a single thing called a 2019-2020. An en dash instantly signals a range. Similarly, an em dash that is spaced—like this — can look like a hyphen with delusions of grandeur, and it interrupts the visual flow. AP style keeps em dashes closed up so they sit tight against the words, preserving the rhythm of the sentence. Consistency matters, too. A publication that mixes spaced and unspaced em dashes, or that uses hyphens for ranges, looks sloppy. Readers may not know the names of these marks, but they notice when something feels off. Clean dash use is part of a professional surface that lets the content speak without distraction. On deadline, editors do not have time to debate every mark, so a house style that follows AP gives everyone a shared default. That default reduces errors and speeds up the editing process.
3 Where writers usually slip
The most common slip is using a hyphen where an em dash belongs. A writer types a quick hyphen to set off a phrase, producing a sentence like The CEO - who was late - apologized. That hyphen is too short and too weak; it reads like a compound word. The fix is an em dash, closed up: The CEO—who was late—apologized. Another frequent error is spacing the em dash. Some writers, influenced by other style guides or by word processors that autoformat, put spaces around it. AP style says no spaces. A third slip is using an en dash for a simple compound that should take a hyphen. For instance, a well–known author should be a well-known author because well and known are single words forming a compound adjective. The en dash is reserved for compounds where one element is already hyphenated or multiword, such as a pre–Civil War era or a New York–based company. Finally, writers sometimes use an en dash for a range but forget to use it consistently, mixing 2019-2020 and 2019–2020 in the same document. That inconsistency is a red flag for editors. Each of these slips is easy to fix once you know the rule, but they persist because the marks look similar and keyboards make them hard to type.
4 Applying the rule on deadline
When you are on deadline, you need a fast way to choose the right dash. Start by asking what the dash is doing. If it is breaking a sentence—setting off an aside, introducing a sharp turn, or marking an interruption—use an em dash. Type it closed up: no space before or after. If it is showing a range, use an en dash. That covers dates, times, page numbers, scores, and any span from one point to another. If it is joining words into a single modifier, use a hyphen. The exception is when one part of that compound is already hyphenated or made of two or more words; then use an en dash. For example, a company based in New York is a New York–based company. A period before the Civil War is a pre–Civil War period. On deadline, you may not have time to look up every compound, but you can apply the two-word test: if the element before or after the dash contains a space or a hyphen, use an en dash. Otherwise, use a hyphen. For em dashes, remember that AP style keeps them tight. If your keyboard lacks an em dash, you can often insert one from a symbol menu or use a keyboard shortcut. Do not substitute a spaced en dash unless your publication's style explicitly allows it. Speed comes from habit, so practice these choices until they are automatic.
5 Legitimate exceptions
There are times when the strict AP rule bends. One common exception is when a font or publishing system does not support the em dash. In that case, a spaced en dash may be used as a fallback, but it should be a last resort. Some publications, especially in certain academic or literary contexts, prefer spaced en dashes for parenthetical breaks. That is a house style choice, not AP style. If you are writing for a publication that follows AP, stick with the closed-up em dash. Another exception involves ranges in certain scientific or technical contexts where a hyphen is conventional, such as in some serial numbers or phone numbers. Those are not true ranges and follow their own conventions. Also, when a range is expressed with from or between, use to or and instead of a dash: from 2019 to 2020, not from 2019–2020. The dash is not needed when the preposition already does the work. Finally, in very short ranges, such as a score of 3–2, an en dash is still correct, but some sports styles use a hyphen. Again, know your style guide. The key is that exceptions are deliberate and consistent, not accidental. If you deviate from AP, do so for a reason and apply it uniformly throughout the piece.
6 A worked example from the copy desk
Imagine a draft sentence: The senator - who had served from 2001-2009 - was known for her pre-war stance. The copy editor sees three dash problems. First, the hyphens around the parenthetical phrase should be em dashes, closed up. Second, the range 2001-2009 should use an en dash. Third, pre-war is a compound that, in this context, refers to a specific war; if the war is named and multiword, it would take an en dash, but here it is a simple prefix, so a hyphen is fine. However, if the sentence were about the pre–Civil War era, the en dash would be correct. The editor revises: The senator—who had served from 2001–2009—was known for her pre-war stance. Note that from is used with to, not with a dash, so the range is expressed as from 2001 to 2009 if the preposition is kept. But if the dash is used, it stands alone: 2001–2009. The editor might also query whether pre-war is the best term, but that is a style choice. The final sentence reads cleanly, with each dash doing its proper job. This example shows how a single sentence can contain all three marks and how a copy editor sorts them out quickly by applying the rule: em for breaks, en for ranges and multiword compounds, hyphen for simple compounds.
7 Quick reference and related rules
Keep this mental cheat sheet: em dash (—) for breaks, closed up; en dash (–) for ranges and for compounds with a multiword or hyphenated element; hyphen (-) for simple compounds and word division. Related rules include the use of from and between with ranges: use to or and, not a dash. Also, do not use a dash to introduce a list; a colon does that job. Do not use a dash where a comma, semicolon, or parenthesis would be more appropriate. Dashes are strong medicine; use them sparingly for maximum effect. In AP style, the em dash is also used to attribute a quotation: “I have a dream”—Martin Luther King Jr. Note the closed-up em dash. For en dashes in compounds, remember that the en dash links elements of equal weight, while the hyphen links elements that form a single unit. For example, a Los Angeles–based artist takes an en dash because Los Angeles is two words. A well-known artist takes a hyphen because well and known form a single modifier. Finally, when in doubt, consult the AP Stylebook or your publication's style guide. Consistency is the goal. If you apply these rules, your copy will be cleaner, clearer, and more professional, and your editors will thank you.