The Chicago Manual of Style is the essential guidebook for writers, editors, and publishers. The manual’s contents are extensive, covering not only substantial publishing issues but also minuscule details about formatting and style as well. One may feel overwhelmed by the vast information that this manual provides, so today, we’re breaking down the top CMoS punctuation rules that you should know.
“A period marks the end of a declarative or imperative sentence” (6.12).
~When a full sentence is in parentheses, the period belongs within the closing parenthesis (6.13).
Example: (She had never met the strange man in person.)
~When parentheses end as part of another sentence, the period is placed outside of the closing parenthesis (6.13).
Example: The woman wrote with fervor (she could hardly contain her love).
“The comma . . . indicates the smallest break in sentence structure” (6.16).
~A dependent clause must be followed by a comma when placed before an independent clause (6.24).
Example: Larry was early to the meeting, so he smoked a cigarette while he waited.
~Conjunctions do not need separation by a comma if a dependent clause comes between other clauses that are connected by a coordinating conjunction (6.26).
Example: “She claimed to have seen the whole film, but when we pressed her for details, she failed to recall the name of Rhett and Scarlett’s only child” (6.26).
~Nonrestrictive clauses that are preceded by “which” should be separated by commas (6.27).
Example: The church bell, which towered above the city’s industrial buildings and towers, chimed loudly every morning and night.
~A nonrestrictive word, phrase, or clause that is an apposition to a noun should be separated by commas (6.28).
Example: The fantasy writer, Holly Black, published the final book in The Folk of the Air trilogy last year.
~A restrictive phrase does not require separation by commas (6.29).
Example: The man holding the orange cat is my uncle.
~Participial phrases that begin a sentence are usually separated by a comma (6.30).
Example: Humiliated by the scandal, the councilman resigned from his position in city government.
~An adverbial phrase does not normally need a comma unless it begins a sentence (6.31).
Example: Without losing her nerve, the deputy followed trail of blood.
~A comma is not needed for introductory adverbial phrases in an inverted sentence (6.31).
Example: “Before the footlights stood one of the most notorious rakes of the twenty-first century” (6.31).
“In regular prose, a semicolon is most commonly used between two independent clauses not joined by a conjunction to signal a closer connection between them than a period would” (6.56).
~Conjunctive verbs such as “however,” “thus,” “besides,” and so on elicit a semicolon and not a comma (6.57).
Example: The graduate knew that he was about to begin a new chapter in his life; however, he would miss university life.
~Semicolons can be used in place of commas when a series of items contains internal punctuation (6.60).
Example: The results of the race were as follows: first place, Warren Brady; second place, Tyra Neil; third place, Randy Maxwell.
Parentheses and Brackets
“Parentheses—stronger than a comma and similar to the dash—are used to set off material from the surrounding text” (6.95).
~When an occasion arises to use parentheses within parentheses, replace the inner parentheses with brackets (6.97, 6.101).
Example: (The bestseller’s first edition  was followed by a second edition  that contains a special note from the author.)
~Commas, semicolons, and colons should always come after the closing parenthesis, not before (6.98).
Example: Robby never cheated on his wife (his high school sweetheart), but he thought about it.
~If belonging to the parenthetical matter, question marks and exclamation points may proceed the closing parenthesis (6.98).
Example: “Come on in (quietly, please!) and take a seat” (6.98).
~Brackets are used instead of parentheses to enclose material that does not develop the surrounding text (6.99).
Example: The group [The Puffs] was a secret society at Chilton.
For extensive information on punctuation formatting and other matters regarding style and usage, reference The Chicago Manual of Style, 17th edition.