Punctuation is usually taught as decoration, a set of fussy rules for school essays. It is better understood as traffic signals for the reader. It tells them where to pause, what belongs together, and what's an aside. Get it wrong, and the reader takes the wrong turn.
The $5 million comma
Maine's law said overtime pay did not apply to:
"canning, processing, preserving, freezing, drying, marketing, storing, packing for shipment or distribution" of certain foods.
Read it two ways:
- "packing for shipment or distribution" = one activity, packing (whether for shipment or for distribution). The drivers don't pack, so they're owed overtime.
- "packing for shipment, or distribution" = two activities. Distribution is exempt, so the drivers aren't owed overtime.
There was no comma before "or distribution." A lower court had sided with the dairy, but the appeals court found the sentence ambiguous, and because Maine reads unclear wage laws in workers' favour, it ruled for the drivers. Maine later rewrote the law with semicolons. The comma in question, the one before the final "and" or "or" in a list, is the serial comma or Oxford comma. Some style guides want it and some don't, so the honest lesson isn't "always use it." It's this: when a list could be misread, punctuate so it can't be.
I'd like to thank my parents, Ayn Rand and God.
I'd like to thank my parents, Ayn Rand, and God.
The comma that saves Grandma
The most famous example is also the simplest:
- Let's eat Grandma.
- Let's eat, Grandma.
When you speak to someone by name (Grandma, Sam, sir), a comma sets the name apart. Without it, the person becomes the object of the verb.
Commas that say "just one" or "one of several"
This one changes facts, not just tone.
- My brother who lives in Paris is a chef. No commas. "Who lives in Paris" tells you which brother, so you probably have more than one.
- My brother, who lives in Paris, is a chef. With commas, "who lives in Paris" is extra information about your only brother.
Grammarians call the first kind restrictive (it narrows down which one) and the second non-restrictive (it adds a side note). Commas around a phrase mean "you could lift this out and the sentence would still point to the same person."
American style guides often add a related preference: use that for the narrowing kind ("the report that I sent") and which, with commas, for the side-note kind ("the report, which I sent on Monday,"). British writers use which for both more freely, and linguists point out this was always more of a style preference than a rule.
Apostrophes: one owner or many?
- My sister's friends = the friends of one sister.
- My sisters' friends = the friends of two or more sisters.
- My sisters, friends = you're talking to your sisters, and calling them friends.
Hyphens: what goes with what
A hyphen glues words into a single description before a noun.
| Without | With |
|---|---|
| a man eating shark (a man, eating a shark) | a man-eating shark |
| a small business owner (a short person who owns a business) | a small-business owner |
| twenty odd people | twenty-odd people (about twenty) |
| I need to resign (quit) | I need to re-sign (sign again) |
A myth worth knowing: you may have read that NASA's Mariner 1 rocket was destroyed in 1962 because of a missing hyphen. Arthur C. Clarke called it "the most expensive hyphen in history." It's a good story, but the missing mark was actually a bar over a symbol in a handwritten maths formula, not a hyphen.
Colons, semicolons and dashes
- A colon means "here's what I mean": She had one goal: to finish. What comes after explains or lists what came before.
- A semicolon joins two full sentences that are closely linked: The shop was closed; we went home. It's a stronger pause than a comma and a softer one than a full stop.
- A dash marks a sharp aside or a turn. It's the most informal of the three, so use it sparingly in formal writing.
The period in a text message
Punctuation carries tone, not just structure. A small 2016 study from Binghamton University found that young adults rated text replies ending in a full stop ("Okay.") as less sincere than the same replies with no punctuation ("Okay"). The same effect didn't show up in handwritten notes. In texting, the line break has become the default ending, so a full stop can read as curt.
None of that makes the full stop wrong. It just means each medium has its own conventions. In an email or a report, leaving off the full stop looks careless. In a text, adding one can look cold.
Scare quotes say "I don't believe this"
- We have fresh fish.
- We have "fresh" fish.
Quotation marks around a word that isn't a quotation often signal doubt or irony. That is exactly why "fresh" fish is not a sign you want in a shop window.
The panda
A best-selling book on punctuation takes its title from an old joke. A panda walks into a café, eats a meal, fires a gun and leaves. The waiter checks a badly punctuated wildlife manual, which says the panda "eats, shoots and leaves." Without the comma, it eats shoots and leaves. Lynne Truss's Eats, Shoots & Leaves (2003) made that joke famous. The writer Ursula K. Le Guin had popularized it in her 1998 book Steering the Craft.
The takeaway
Punctuation is a set of signals that tell readers how a sentence fits together, and moving a single mark can change who is speaking, how many people you mean, what is being described, or whether a law applies. The commas around a phrase show whether it narrows things down or just adds information. Apostrophes show who owns something, hyphens show which words describe something together, and even the full stop carries tone in a text. When a sentence could be read two ways, punctuate so it can only be read one way.
Try this: find the last list you wrote, in an email or a document, and read it as a stranger would. Could any two items be read as one? If so, add the comma, or rewrite the list so that misreading is impossible.
Sources & Further Reading
Sources
- O'Connor v. Oakhurst Dairy (US Court of Appeals for the First Circuit, March 2017), the "For want of a comma" opening, the $5 million settlement and Maine's later rewording with semicolons: Wikipedia, "Serial comma," citing the court opinion, The New York Times and The New Yorker.
- Restrictive and non-restrictive clauses, and the that/which preference (proposed by Goold Brown in 1851, championed by H. W. Fowler in 1926): Wikipedia, "Restrictiveness" and "English relative clauses."
- Mariner 1 and the "most expensive hyphen": Wikipedia, "Mariner 1" (the error was a missing overbar in a formula).
- Gunraj et al., "Texting insincerely: The role of the period in text messaging," Computers in Human Behavior (2016), via Wikipedia, "Full stop."
- Eats, Shoots & Leaves (Lynne Truss, 2003) and the panda joke's popularization by Ursula K. Le Guin in Steering the Craft (1998): Wikipedia, "Eats, Shoots & Leaves."
Go deeper
- 📘 Eats, Shoots & Leaves by Lynne Truss: a funny, passionate (and strongly opinionated) defence of punctuation
- 📘 Between You & Me: Confessions of a Comma Queen by Mary Norris: a New Yorker copy editor on commas, hyphens and the people who care about them
- 🌐 Purdue OWL: Punctuation: clear, free reference pages for every mark
- 🌐 Related pieces in this library: Grammar Without Tears and Plain Writing, this category