Punctuation
Table of contents
Guidelines for using those familiar dots, dashes, and squiggles.
Colons
Colons and capitalization
If you’re using a colon within a self-contained sentence, the first word following the colon should remain lowercase (unless that word is a proper noun).
- Example: We use three metrics in our analysis: quality, cost, and speed.
Commas
Clauses
If two independent clauses are separated by a coordinating conjunction, use a comma unless both clauses are very short.
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Long: We built everything slowly over the course of several months, and it all seems to work so far.
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Short: We worked too quickly and it all fell apart.
If a dependent clause and an independent clause are separated by a coordinating conjunction, don’t use a comma unless the sentence would be unclear without it.
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Clear without comma: The vacuum of space is cold and will kill you almost instantly.
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Needs comma for clarity: Vacuums are unforgiving in space, but clean carpets marvelously well.
Introductory phrases
Use a comma after an introductory phrase (like however or furthermore or on the other hand).
- Example: Despite this, we reached the mouth of the cave by sundown.
Serial commas
Use serial commas (also known as Oxford commas).
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No: I love my parents, Godzilla and Wonder Woman.
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Yes: I love my parents, Godzilla, and Wonder Woman.
Dashes and hyphens
Em dashes
You can use em dashes—just don’t put spaces between the em dash and the words surrounding it.
Compound modifiers
Use a hyphen between compound modifiers unless the first word is in adverb ending in -ly.
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Hyphenated: well-learned students
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Not hyphenated: easily performed tasks
Compound words
Sometimes it’s helpful to hyphenate compound words to avoid ambiguity. A good rule of thumb is to use a hyphen for compound words that aren’t widely used or that could be mistaken for another word.
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Hyphenated: re-create, pre-date
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Not hyphenated: remix, prepaid
Prefixes
Use a hyphen between a prefix and a proper noun or abbreviation.
- Example: Files with non-JSON syntax are unsupported.
Suspended hyphens
Use suspended hyphens to list several hyphenated compounds in a row.
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Example: The craft fair offers soap- and basket-making classes.
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Example: Bills come in one-, five, and twenty-dollar increments.
Parentheses
End punctuation
Place end punctuation marks (like commas and periods) outside parentheses unless the punctuation is part of the parenthetical text or the parentheses contain a standalone sentence.
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Outside parentheses: It’s legal to own a zebra in certain states (like Nevada).
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Inside parentheses: It’s legal to own a zebra in certain states. (Nevada is one of them.)
Mid-sentence parentheticals
Parenthetical statements are useful for mid-sentence examples and short asides (like this one), but excessively long and complicated parentheticals may be better of rewritten as their own sentence (or else you’ll end up with a meandering, monstrous behemoth of a sentence that seems to go on and on and on with no end in sight).
Semicolons
Avoid overuse
Semicolons are your friend; however, like any friend, you might get sick of them if they show up too frequently. Tread carefully and wisely.
Clauses
You can use a semicolon to connect two independent clauses.
- Example: The film received terrible reviews; none of the reviewers could even stay awake through the whole thing.
You can also use a semicolon to connect two independent clauses connected by a conjunctive adverb (like however or similarly) or, occasionally, a regular old conjunction (like and or but or if).
- Example: Most mountains aren’t as tall as Everest; however, they still pose a suitable challenge for climbers.
But consider carefully whether you really need a semicolon or if you’d be better off breaking things into two separate sentences.
Lists
When commas alone won’t suffice, you can use semicolons to separate complex items in a series or list.
- Example: Our team includes May, a prestigious researcher; Brendan, a tenacious explorer; and Wally, a skilled analyst.