Hyphens, En Dashes, and Em Dashes in Academic Writing: Rules and Examples

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Key Takeaways

• A hyphen joins words and word parts; an en dash shows a range or connects equal terms; an em dash sets off or interrupts a thought.
• Number ranges, dates, and page spans should use an en dash, not a hyphen — a frequent error across all three disciplines.
• Always confirm the target journal’s specific style requirements before finalizing punctuation, since house style can override general guidance.

Contents

• Introduction: Why Punctuation Marks Matter in Academic Writing
• What Is the Difference Between Hyphens, En Dashes, and Em Dashes?
• The Hyphen (-): Definition and Core Uses
• The En Dash (–): Definition and Core Uses
• The Em Dash (—): Definition and Core Uses
• How Do You Type En Dashes and Em Dashes on a Keyboard?
• Hyphen vs En Dash vs Em Dash: Quick Comparison Table
• What Are the Most Common Dash and Hyphen Mistakes in Research Papers?
• Should You Use Em Dashes in Formal Academic Writing?
• Frequently Asked Questions

Introduction: Why Punctuation Marks Matter in Academic Writing

Hyphens, en dashes, and em dashes look similar but perform very different grammatical jobs. Using the wrong one signals carelessness in a research paper or dissertation. Carelessness in punctuation can prompt examiners or peer reviewers to question carelessness elsewhere in the methodology.

This guide explains each mark, shows how the rules apply across social science, biomedical, and physical science writing, and summarizes what the major style guides (APA, MLA, Chicago, and AMA) require.

What Is the Difference Between Hyphens, En Dashes, and Em Dashes?

A hyphen (-) joins words or word parts, an en dash (–) shows a range or a connection between two equal terms, and an em dash (—) sets off or interrupts a thought. The three marks increase in length and in the size of the grammatical unit they connect.

• Hyphen (-): the shortest mark; joins compound words, prefixes, and numbers.
• En dash (–): roughly the width of the letter “N”; links ranges, scores, and paired terms.
• Em dash (—): roughly the width of the letter “M”; marks a break, aside, or emphatic pause.

The Hyphen (-): Definition and Core Uses

A hyphen joins two or more words so they function as a single unit, or attaches a prefix or suffix to a root word. It is the shortest of the three marks and the one used most often in everyday academic prose.

Compound Adjectives Before Nouns

When two or more words work together to modify a noun that follows them, they are usually hyphenated.

• a well-documented bias, a cross-cultural study, a middle-income household
• a double-blind trial, a high-risk patient, a well-tolerated dose
• a low-frequency signal, a two-dimensional lattice, a steady-state reaction

Prefixes, Suffixes, and Compound Nouns

Most prefixes attach without a hyphen (nonlinear, reevaluate), but a hyphen is kept when omitting it would create confusion, a double vowel clash, or an awkward reading.

• co-author, self-report, post-intervention (avoids “postintervention”)
• pre-existing condition, re-infection
• re-orient, sub-atomic (style-dependent), anti-aliasing

Hyphens in Numbers, Fractions, and Ratios

• twenty-five participants, a two-thirds majority
• a 3-year follow-up, a one-third reduction in relapse rate
• a 95-percent confidence bound, a first-order approximation

Quick reference

Example Phrase	Why a Hyphen Is Used
a hard-to-reach population	Compound adjective before the noun “population”
a 12-week treatment period	Number-plus-noun compound modifier
a wave-particle duality	Two nouns joined to form one concept

The En Dash (–): Definition and Core Uses

An en dash is longer than a hyphen and shorter than an em dash. It typically shows a range of values or links two terms that remain grammatically independent, such as two cities or two researchers’ names.

Showing Ranges in Numbers, Dates, and Pages

• the 1990–2020 period, respondents aged 18–65
• a follow-up of 6–12 months, see pp. 112–118
• a wavelength of 400–700 nanometers, Figures 3–5

Connecting Related but Independent Terms

• the Mumbai–Delhi migration corridor, the teacher–student relationship
• a dose–response relationship, the gene–environment interaction
• the Bose–Einstein condensate, the stress–strain curve

Quick reference: en dash examples

Example Phrase	Context
the 2015–2019 survey wave	Range of years in a longitudinal study
a 5–10 mg dosage range	Range of drug dosages in a protocol
the Michelson–Morley experiment	Two independent researchers named jointly

The Em Dash (—): Definition and Core Uses

An em dash is the longest of the three marks. It sets off a parenthetical remark, marks a sudden break in a sentence, or adds emphasis in a way that is more forceful than a comma or parentheses.

Setting Off Parenthetical Information

• The sample—drawn from three urban districts—was not nationally representative.
• Adverse events— most of them mild—were reported in 1.2% of patients.
• The detector—calibrated the day before the run—showed no baseline drift.

Indicating a Break, Pause, or Emphasis

• The policy achieved its stated goal—but at a considerable social cost.
• The trial was halted early—the safety signal was too strong to ignore.
• The model fit the data well—until temperatures exceeded 400 K.

Quick reference: em dash examples by discipline

Example Sentence Fragment	Function of the Em Dash
the finding—though preliminary—is consistent	Sets off a qualifying aside
the biomarker—elevated in 80% of cases—predicted relapse	Inserts supporting data mid-sentence
the anomaly—undetected until 2021—reshaped the model	Marks a dramatic interruption

How Do You Type En Dashes and Em Dashes on a Keyboard?

On Windows, hold Alt and type 0150 on the numeric keypad for an en dash or 0151 for an em dash. Both the en and em dashes are available in the Symbol list under the Insert menu. On Mac, press Option+Hyphen for an en dash and Shift+Option+Hyphen for an em dash. Word also auto-converts typed hyphens in many cases.

If autocorrect produces the wrong mark, use Insert > Symbol, or the keyboard shortcuts above, and disable autoformatting under File > Options > Proofing if it keeps guessing wrong.

Hyphen vs En Dash vs Em Dash: Quick Comparison Table

Mark	Symbol	Relative Length	Typical Use
Hyphen	–	Shortest	Joins compound words, prefixes, numbers
En dash	–	Medium	Ranges, scores, paired independent terms
Em dash	—	Longest	Parenthetical asides, breaks, emphasis

What Are the Most Common Dash and Hyphen Mistakes in Research Papers?

The most common mistakes are using a hyphen instead of an en dash in number ranges, overusing em dashes where commas would read more formally, and inconsistent spacing around dashes within the same manuscript.

• Writing “aged 45-67” with a hyphen instead of “aged 45–67” with an en dash
• Using a hyphen for a score or vote count, such as “the committee voted 7-2” instead of “7–2”
• Mixing spaced and unspaced em dashes within the same document
• Hyphenating a compound adjective that comes after the noun it modifies, such as “the patient was 45-years-old” (no hyphen needed there) versus “a 45-year-old patient” (hyphen needed)
• Using an em dash where a colon or semicolon would better suit a formal journal’s house style

Should You Use Em Dashes in Formal Academic Writing?

Yes, in moderation. Most style guides permit em dashes for asides or emphasis, but many journals in the biomedical and physical sciences prefer commas, parentheses, or semicolons for a more formal, data-focused tone.

• Use an em dash sparingly, generally no more than once or twice
• Check the target journal’s author guidelines before submission, since some prohibit em dashes entirely
• Use a comma or parentheses ( ) when the aside is short and does not need strong emphasis
• Currently, overuse of em dashes is widely perceived as a sign of AI-generated text. I would advise limiting them to 1-2 in an entire paper.

Frequently Asked Questions

What is the difference between a hyphen and a dash?

A hyphen joins words or word parts into a single unit, while a dash (either an en dash or an em dash) connects or separates larger grammatical elements such as ranges, clauses, or asides.

When should I use an en dash instead of a hyphen?

Use an en dash for number ranges, date spans, page ranges, and terms that combine two independent, equal elements, such as a dose–response relationship or a New York–Dallas route.

Is it correct to use three hyphens instead of an em dash?

No; three hyphens (—) are a typewriter-era substitute. Most word processors convert them automatically, but the final manuscript should show a true em dash (—), not triple hyphens.

Can I use an em dash in a scientific research paper?

Yes, sparingly, to flag an unexpected result or add a brief aside, but many biomedical and physical science journals prefer commas, parentheses, or semicolons for a more formal tone.

How do I insert an en dash automatically in Microsoft Word?

Type a number, a space, a hyphen, a space, and another number (such as “1990 – 2020”); Word’s AutoCorrect usually converts the hyphen to an en dash once you continue typing.

Why do compound adjectives need a hyphen before a noun?

A hyphen prevents misreading by showing that two or more words act as a single descriptive unit before the noun, such as a “small-animal hospital” (a hospital for small animals) instead of “small animal hospital” (an animal hospital that is small in size).