Punctuation is the use of conventional (and agreed-upon) marks to guide readers through our written text. We begin with a common set of simple rules for punctuation based on the concepts that we have discussed throughout this textbook. In other words, we believe that punctuating sentences should always be based on an understanding that sentences are always made up of clauses, phrases, and words. We have organized our basic punctuation rules with this in mind.

9 Basic Rules of Punctuation

These basic rules center in part on the concept of Sentence Variety. We also believe that punctuation, despite its clear rules, is also rhetorical, so we don't consider these rules as wholly prescriptive (or "written in stone"). Punctuation should also be understood in context. The rules described below are by no means comprehensive, but we believe that these basic rules will cover 90% of the writing that you do, and understanding them will help you make considered choices for the other 10%, as well as other stylistic choices. In other words, these 9 Basic Rules should serve as a starting point for understanding the ways that punctuation can be considered a rhetorical choice.

Rule 1 - Independent clause. Independent clause.

Example: The telephone rang. He rushed to answer it.

A period is an end stop and the primary marker for separating independent clauses. This would also include other end punctuation, such as the question mark and the exclamation point.

Rule 2 - Independent clause; independent clause.

Example: The dog barked; the letter carrier ran.

A semicolon can act like a soft period and separate independent clauses.

Rule 3 - Independent clause; conjunctive adverb, independent clause.

Example: Parking is scarce; therefore, many drivers park illegally.

Example: Parking is scarce; many drivers, therefore, park illegally.

Building on Rule 2, a conjunctive adverb can coordinate independent clauses, and since it separates independent clauses, you need to mark the end of the clause before the conjunctive adverb with a semicolon. A comma after the conjunctive adverb signals the beginning of the next independent clause. Remember, as an adverb, the conjunctive adverb can move around in the second independent clause, but the semicolon still signals the end of the first independent clause.

Rule 4 - Independent clause, coordinating conjunction independent clause.

Example: Jenny ran to first base, but the shortstop threw her out.

A coordinating conjunction when preceded by a comma is a KEY MARKER for independent clauses. As coordinated clauses, the punctuation pattern is a variation on a coordinated list: the end of the first item (clause) is marked with a comma. It's important to remember that the comma always occurs before the coordinator, which then adheres to the second (or final) item (clause) in the "list."

Rule 5 - Dependent clause, independent clause.

Example: When the clock struck twelve, the mouse ran down.

When a dependent clause precedes an independent clause, you signal the end of the dependent clause with a comma. While this occurs most commonly at the beginning of a sentence, with (normally) an adverbial subordinate clause occupying the introductory position, followed by an independent clause, this pattern can happen anywhere in a sentence. So this introductory clause (or concluding clause) should be punctuated as a non-restrictive clause.

Rule 5A (variation) - Independent clause dependent clause.

Example: The mouse ran down when the clock struck twelve.

A variation on Rule 5 is when a dependent clause follows an independent clause without punctuation. Because this dependent clause is adverbial (most often a subordinate clause), it is not the same thing as a restrictive clause (see Rule 8), and for this reason, when a dependent clause follows an independent clause, convention does not require a comma to separate the clauses. However, stylistically, you can make a choice to use a comma to separate the clauses for a variety of reasons: pace, emphasis, non-restriction, etc. Using a comma to separate an independent clause from a dependent clause in this context is not grammatically incorrect.

Rule 6 - Adverbial nonfinite verb phrase or prepositional phrase, independent clause.

Example: To do well in school, you must study hard.

Example: For success in school, you must study hard.

Example: You must study hard, for perceived success in school.

Similar to the introductory clause, an adverbial nonfinite verb phrase or prepositional phrase in an introductory position normally calls for the use a comma to separate it from the independent clause. While some offer a word-count rule for this introductory phrase (i.e., "Use a comma to separate an introductory phrase that is more than four words long"), the most effective (and most grammatical), is to get into the habit of using a comma whenever you use an introductory adverbial nonfinite verb phrase or prepositional phrase. Similarly, if an adverbial non-finite verb phrase or prepositional phrase concludes a sentence, the phrase can be preceded by a comma.

Rule 7 - Independent, nonrestrictive dependent clause or phrase, clause. OR – nonrestrictive clause or phrase – OR (nonrestrictive clause or phrase)

Example: Subordinate clauses, because they are adverbial, or non-restrictive, can move about in a sentence.

Example: Jane's father, who is in his eighties, is an octogenarian.

Example: Jane's father - well into his eighties - is an octogenarian.

Example: Jane's father (pushing ninety) is an octogenarian.

A non-restrictive clause or phrase, in contrast to restrictive, is extra or supplemental information. Since this information is not required, you signal its supplemental status by placing a comma before and after the non-restrictive clause or phrase. To extend this rule slightly, if the non-restrictive clause/phrase is at the beginning of the sentence, you use a single comma at the end of the clause/phrase; similarly, if the non-restrictive phrase/clause is at the end of the sentence, you use a single comma before it. 

This rule applies to all dependent clauses, including non-restrictive adjectival relative clauses or, even, nominal clauses, but the adverbial subordinate clause is the most common, since it can move about in a sentence. This means that if you place a subordinate clause between the subject and the main verb phrase of another clause, you must set it apart using a comma before and after the subordinate clause.

Finally, a stylistic consideration is the use of different punctuation marks that function like a set of paired commas. While paired commas is the accepted and conventional mark, you can also use a double dash or a parentheses to achieve the same effect. Which set of marks you use should be a considered choice, as each can serve different ends for guiding your readers through your text.

Rule 7A (variation) - Independent restrictive clause/phrase clause.

Example: A woman who is in her eighties is an octogenarian.

Another example of a "non-punctuation" rule. A restrictive dependent clause or phrase is information that is required to define or clarify the element that it is next to, so it does not use punctuation. More often than not, restrictive clauses or phrases are adjectival. Since the information is required to define or clarify its nominal, you should not use any punctuation. (See Some Comma Rules for more information)

Rule 8 - Independent clause: (to introduce a list or a restatement of the previous clause)

Example: The girl's life was extremely hectic: school, work, caregiving, and studying.

Example: The girl's life was extremely hectic: mornings were spent in school; afternoons were spent at work; evenings were spent taking care of her invalid grandmother; and nights were spent studying.

Example: The girl's life was extremely hectic: she was on the move constantly from morning to night.

A colon most commonly signals a list or restatement of an independent clause.

Rule 9 - Commas in a series

Example: The girl's life was extremely hectic: school, work, caregiving, and studying.

Example: The girl's life was extremely hectic: mornings were spent in school; afternoons were spent at work; evenings were spent taking care of her invalid grandmother; and nights were spent studying.

In a list or series (words, phrases or clauses, you separate simple items using commas, and separate complex items (such as a list of clauses following a colon) using semicolons. This will be discussed in more detail in Some Comma Rules.

As we said, these rules by no means cover all possibilities for punctuation in the English language, but they will probably cover 90% percent of them. More importantly, they are adaptable and offer a base for punctuating effectively.