Commas

This is Unit Seven of College Composition. Unit Six ended by checking a paragraph's structure sentence by sentence. This unit applies the same habit to the most common mark of punctuation, the comma. Carry one idea through this lecture. A comma belongs where a rule calls for it, not wherever a speaker would pause, and a single comma can change what a sentence claims. The last entry in this unit shows that change. By the end you will be able to place commas with clauses, introductions and series. To set off nonessential information and leave essential information alone. To use commas with transitions, quotations and dates. And to remove the commas no rule supports.

Five entries on the comma's main patterns: joining clauses, after introductions, in a series, and between equal adjectives.

Commas show what belongs together.

CMP 0151 What Commas Do

Commas mark brief pauses within a sentence and show readers which words belong together. Most comma rules fall into a few patterns: before a conjunction joining clauses, after an introductory element, around nonessential information, and between items in a series. Do not place commas by breath alone; many errors come from commas added wherever a speaker would pause.

Two clauses and a conjunction.

CMP 0152 Commas With Coordinating Conjunctions

Use a comma before a coordinating conjunction that joins two independent clauses. "Businesses are growing, and unemployment is down." Each side has a subject and a verb, so the comma goes before and. Without the conjunction, the comma alone makes a comma splice, and without the comma, long clauses can run together.

An opening before the main clause.

CMP 0153 Commas After Introductory Elements

Use a comma after an introductory word, phrase or clause that comes before the main clause. "After class is over, we should review our notes"; "Shuffling his feet, he waited"; "However, nothing has changed." A missing comma after a long introduction can make readers misread the subject.

Three or more items.

CMP 0154 Commas in a Series

Use commas between items in a series of three or more. "He read the notes, emails, memos, and reports." The comma before and is called the serial or Oxford comma, and it prevents misreading. Some style guides omit the serial comma; whichever you choose, use it consistently.

Two equal adjectives.

CMP 0155 Coordinate Adjectives

Use a comma between two adjectives that equally describe the same noun. "It was a stressful, sleepless night." Test by reversing the adjectives or putting and between them; if the sentence still makes sense, use the comma. "The white frame house" takes no comma, because frame house is a unit and the adjectives are not equal.

Four entries on the most consequential comma decision: whether information is essential, which or that, and appositives. A test for deciding comes later in this lecture.

Extra detail, set off.

CMP 0156 Nonessential Information

Nonessential information adds detail but is not needed to identify what the sentence means, and it is set off with commas. "The department chair, who teaches welding, wrote the report." There is one chair, so the clause only adds detail. Nonessential information needs commas on both sides unless it ends the sentence.

Information that identifies.

CMP 0157 Essential Information

Essential information is needed to identify what the sentence refers to, and it takes no commas. "Faculty who teach auto mechanics requested new equipment." Only those faculty made the request, so the clause narrows the meaning. Commas around essential information change the claim, here making it about all faculty.

Which and that.

CMP 0158 Which and That

In standard usage, which introduces nonessential clauses, with commas, and that introduces essential clauses, without them. "The labs, which were built long ago, need updates" describes all the labs; "The labs that were built long ago need updates" picks out some. If you can remove the clause without changing the meaning, use which and commas.

A noun that renames.

CMP 0159 Appositives

An appositive is a noun phrase that renames the noun beside it, and it follows the same essential and nonessential rule. "Diana Wong, the clinic's director, spoke first" sets off a nonessential appositive; "the expert Stacy James" needs no commas, because the name identifies which expert. A title before a name is usually essential; a description after a name is usually not.

Four entries on commas with transitional words, contrasts, quotations, and dates, titles and addresses.

However, therefore and for example.

CMP 0160 Commas With Transitional Expressions

Transitional words such as however, therefore and for example are set off with commas. At the start of a sentence: "However, demand held steady." In the middle of a clause: "Demand, however, held steady." Between two independent clauses, the comma before however must become a semicolon.

A contrast at the end.

CMP 0161 Contrasts and Shifts at the End

Use a comma to set off a contrasting element or a distinct shift at the end of a sentence. "I am brave, not reckless"; "You are coming to the meeting, aren't you?" The comma signals that the sentence turns. Without the comma, the contrast can blur into the main clause.

Signal phrase and quotation.

CMP 0162 Commas With Quotations

Use a comma between a signal phrase and a direct quotation. "As the report states, “The labs are outdated.”" The comma separates the writer's words from the quoted words. An indirect quotation, introduced by that, takes no comma: "The report states that the labs are outdated."

Dates, titles and addresses.

CMP 0163 Numbers, Dates, Titles and Addresses

Commas separate the parts of full dates, addresses, and titles that follow a name. "She died on August fifth, two thousand nineteen, in Ohio"; "Diana Wong, M.D., practices obstetrics"; a city and state take a comma between them. The comma after the year or the state is easy to forget when the sentence continues.

Seven entries on unnecessary commas, a test for essential information, and revising a paragraph's commas, ending with a comma that changes meaning. The opening idea is paid off at the last.

A long subject.

CMP 0164 No Comma Between Subject and Verb

Do not put a comma between a subject and its verb, however long the subject is. "Anyone who was still at the party, left when the band stopped" is wrong; delete the comma after party. Long subjects tempt writers to pause; the pause is in the voice, not in the grammar.

Two verbs, one subject.

CMP 0165 No Comma Before a Compound Predicate

Do not put a comma before a conjunction that joins two verbs sharing one subject. "The band stopped after two hours, and took a break" needs no comma, because took has no subject of its own. Ask whether the words after and could stand alone; if not, leave the comma out.

Other needless commas.

CMP 0166 Other Unnecessary Commas

Several other comma placements are errors: after the last item in a series, between compound objects, and before an indirect quotation. "Guests enjoyed the music, and the dancing" and "Reviews say, that the band is the best" both carry needless commas. When unsure, ask which rule calls for the comma; if none does, leave it out.

A test you can run.

CMP 0167 Deciding Essential or Nonessential

Deciding whether information is essential is a test you can run. Find the clause or phrase, often one beginning with who, which or that. Remove it and reread. If the meaning is unchanged, it is nonessential: set it off with commas, with a comma at both ends, and use which for a clause. If removing it changes the meaning or makes it too general, it is essential: no commas, and that for a clause. The test depends on context. "My brother who lives in Denver" is essential if you have several brothers and nonessential if you have one.

A long sentence, spot by spot.

CMP 0168 Commas in a Long Sentence

Placing commas in a long sentence means checking each candidate spot against a rule. Find the core subject and verb and keep them together. Put a comma after an introductory element. Put a comma before a coordinating conjunction only if it joins two independent clauses. Enclose nonessential elements, separate series items, and remove any comma no rule supports. In the entry's example about a committee's vote, commas go after the introduction and around the which clause, but not before and, because released shares the subject. Long sentences collect extra commas more often than missing ones.

A paragraph, sentence by sentence.

CMP 0169 Revising a Paragraph's Commas

A worked example, constructed for this course, revises a paragraph about a new library. An introductory clause needs a comma after it, while a who clause that identifies which students takes none. A comma between subject and verb is deleted, as is a comma before an indirect quotation introduced by that. Whether the director's name takes commas depends on whether there is only one director. A comma before and joining two verbs with one subject goes, coordinate adjectives get their comma, and the series takes a serial comma if the paper's style uses it. When a choice turns on a fact, look for it in the surrounding passage.

One comma, two claims.

CMP 0170 Commas That Change Meaning

A single comma can change what a sentence claims. "The students, who studied, passed" says every student studied and passed; "The students who studied passed" says only those who studied passed. On revision items, read the comma as part of the claim, and choose the version that says what the writer means.

Look at what you can now do. You can place commas before conjunctions that join clauses, after introductory elements, between series items and between coordinate adjectives. You can tell essential from nonessential information, choose which or that, and punctuate appositives by the same test. You can use commas with transitional words, contrasts, quotations, dates and titles. And you can remove commas no rule supports, revise a paragraph by rule, and read a comma as part of what a sentence claims. Unit Eight turns to the other marks: semicolons, colons, apostrophes, quotation marks and dashes.