A comma splice is a grammatical error in which two independent clauses are joined by only a comma.
INCORRECT: It was 500 miles to the facility, we arranged to fly.
A comma splice can be corrected in several ways.
Substitute a semicolon, a semicolon and a conjunctive adverb, or a comma and a coordinating conjunction.
– It was 500 miles to the facility; we arranged to fly.
– It was 500 miles to the facility; therefore, we arranged to fly.
– It was 500 miles to the facility, so we arranged to fly.
Create two sentences.
– It was 500 miles to the facility. We arranged to fly.
Subordinate one clause to the other.
– Because it was 500 miles to the facility, we arranged to fly.
A. Linking Independent Clauses
Use a comma before a coordinating conjunction (and, but, or, nor, and sometimes so, yet, and for) that links independent clauses.
E.g. The new microwave disinfection system was delivered, but the installation will require an additional week.
However, if two independent clauses are short and closely related—and there is no danger of confusing the reader—the comma may be omitted. Both of the following examples are correct.
CORRECT: The cable snapped and the power failed.
CORRECT: The cable snapped, and the power failed.
B. Enclosing Elements
1) Commas are used to enclose nonessential information (parenthetical elements)
CORRECT: Our new factory, which began operations last month, should add 25 percent to total output.
CORRECT: The technician, working quickly and efficiently, finished early.
CORRECT: We can, of course, expect their lawyer to call us.
2) Yes and no are set off by commas in such uses as the following:
CORRECT: No, I do not think we can finish by the deadline.
3) A direct address should be enclosed in commas.
CORRECT: You will note, Jeff, that the surface of the brake shoe complies with the specification.
4) An appositive phrase (which re-identifies another expression in the sentence) is enclosed in commas.
CORRECT: Our company, Envirex Medical Systems, won several awards last year.
5) Interrupting parenthetical and transitional words or phrases are usually set off with commas.
CORRECT: The report, therefore, needs to be revised.
Commas are omitted when the word or phrase does not interrupt the continuity of thought.
CORRECT: I therefore suggest that we begin construction.
C. Introducing Elements
C.0 Clauses and Phrases.
Generally, place a comma after an introductory clause or phrase, especially if it is long, to identify where the introductory element ends and the main part of the sentence begins.
CORRECT: Because we have not yet contained the new strain of influenza, we recommend vaccination for high-risk patients.
1) A long modifying phrase that precedes the main clause should always be followed by a comma.
During the first series of field-performance tests at our Colorado proving ground, the new engine failed to meet our expectations.
2) When an introductory phrase is short and closely related to the main clause, the comma may be omitted.
In two seconds a 5F temperature rise occurs in the test tube.
3) A comma should always follow an absolute phrase, which modifies the whole sentence.
The tests completed, we organized the data for the final report.
C.1 Words and Quotations.
1) Certain types of introductory words are followed by a comma. One example is a transitional word or phrase (however, in addition) that connects the preceding clause or sentence with the thought that follows.
Furthermore, steel can withstand a humidity of 99 percent, provided that there is no chloride or sulfur dioxide in the atmosphere.
For example, this change will make us more competitive in the global marketplace.
2) When an adverb closely modifies the verb or the entire sentence, it should not be followed by a comma.
Perhaps we can still solve the turnover problem. Certainly we should try. [Perhaps and certainly closely modify each statement.]
3) A proper noun used in an introductory direct address is followed by a comma, as is an interjection (such as oh, well, why, indeed, yes, and no).
Nancy, enclosed is the article you asked me to review. [direct address]
Indeed, I will ensure that your request is forwarded. [interjection]
4) Use a comma to separate a direct quotation from its introduction.
Morton and Lucia White said, “People live in cities but dream of the countryside.”
5) Do not use a comma when giving an indirect quotation.
Morton and Lucia White said that people dream of the countryside, even though they live in cities.
D. Separating Items in a Series
1) Although the comma before the last item in a series is sometimes omitted, it is generally clearer to include it.
Random House, Bantam, Doubleday, and Dell were individual publishing companies. [Without the final comma, “Doubleday and Dell” might refer to one company or two.]
2) Phrases and clauses in coordinate series are also punctuated with commas.
Plants absorb noxious gases, act as receptors of dirt particles, and cleanse the air of other impurities.
3) When phrases or clauses in a series contain commas, use semicolons rather than commas to separate the items.
Our new products include amitriptyline, which has sold very well; and cholestyramine, which was just introduced.
4) When adjectives modifying the same noun can be reversed and make sense, or when they can be separated by and or or, they should be separated by commas.
The aircraft featured a modern, sleek, swept-wing design.
5) When an adjective modifies a phrase, no comma is required.
She was investigating the damaged inventory-control system. [The adjective damaged modifies the phrase inventory-control system.]
6) Never separate a final adjective from its noun.
He is a conscientious, honest, reliable[, not needed here] worker.
E. Clarifying and Contrasting
1) Use a comma to separate two contrasting thoughts or ideas.
The project was finished on time, but not within the budget.
2) Use a comma after an independent clause that is only loosely related to the dependent clause that follows it or that could be misread without the comma.
I should be able to finish the plan by July, even though I lost time because of illness.
F. Showing Omissions
1) A comma sometimes replaces a verb in certain elliptical constructions.
Some were punctual; others, late. [The comma replaces were.]
It is better, however, to avoid such constructions in technical writing.
E. Using with Numbers and Names
1) Commas are conventionally used to separate distinct items. Use commas between the elements of an address written on the same line (but not between the state and the ZIP Code).
Kristen James, 4119 Mill Road, Dayton, Ohio 45401
2) A full date that is written in month-day-year format uses a comma preceding and following the year.
November 30, 2020, is the payoff date.
3) Do not use commas for dates in the day-month-year format, which is used in many parts of the world and by the U.S. military. See also international correspondence.
Note that 30 November 2020 is the payoff date.
4) No commas are used when showing only the month and year or month and day in a date.
The target date of May 2012 is optimistic, so I would like to meet on March 4 to discuss our options.
5) Use commas to separate the elements of Arabic numbers.
6) Use commas to separate the elements of geographical names.
Toronto, Ontario, Canada
7) Use a comma to separate names that are reversed (Smith, Alvin) and commas with professional abbreviations.
Jim Rogers Jr., M.D., chaired the conference. [ Jr. or Sr. does not require a comma.]
F. Using with Other Punctuation
1) Conjunctive adverbs (however, nevertheless, consequently, for example, on the other hand) that join independent clauses are preceded by a semicolon and followed by a comma. Such adverbs function both as modifiers and as connectives.
The idea is good; however, our budget is not sufficient.
2) When a comma should follow a phrase or clause that ends with words in parentheses, the comma always appears outside the closing parenthesis.
Although we left late (at 7:30 p.m.), we arrived in time for the keynote address.
3) Commas always go inside quotation marks.
The operator placed the discharge bypass switch at “normal,” which triggered a second discharge.
4) Except with abbreviations, a comma should not be used with a dash, an exclamation mark, a period, or a question mark.
“Have you finished the project?[no , here]” she asked.
G. Avoiding Unnecessary Commas
A number of common writing errors involve placing commas where they do not belong. As stated earlier, such errors often occur because writers assume that a pause in a sentence should be indicated by a comma.
1) Do not place a comma between a subject and verb or between a verb and its object.
The conditions at the test site in the Arctic[no , here] made accurate readings difficult.
She has often said[no , here] that one company’s failure is another’s opportunity.
2) Do not use a comma between the elements of a compound subject or compound predicate consisting of only two elements.
The director of the design department[no , here] and the supervisor of the quality-control section were opposed to the new schedules.
The design director listed five major objections[no , here] and asked that the new schedule be reconsidered.
3) Do not include a comma after a coordinating conjunction such as and or but.
The chairperson formally adjourned the meeting, but[no , here] the members of the committee continued to argue.
4) Do not place a comma before the first item or after the last item of a series.
The new products we are considering include[no , here] calculators, scanners, and cameras.
It was a fast, simple, inexpensive[no , here] process.
5) Do not use a comma to separate a prepositional phrase from the rest of the sentence unnecessarily.
We discussed the final report[no , here] on the new project.
The hyphen (-) is used primarily for linking and separating words and parts of words. The hyphen often improves the clarity of writing. The hyphen is sometimes confused with the dash, which may be indicated with two consecutive hyphens.
Hyphens with Compound Words
Some compound words are formed with hyphens (able-bodied, over-thecounter). Hyphens are also used with multiword numbers from twentyone through ninety-nine and fractions when they are written out (threequarters). Most current dictionaries indicate whether compound words are hyphenated, written as one word, or written as separate words.
NOTE: These are the notes taken from Alred, Gerald J., Charles T. Brusaw, and Walter E. Oliu. Handbook of technical writing. Macmillan, 2009.