Writers can avoid most errors of punctuation by mastering the following conventions.
1. Introductory words, phrases, and clauses are followed by a comma.
Incorrect: Moreover students are expected to read at least one English classic every six weeks.
Correct : Moreover, students are expected to read at least one English classic every six weeks.
Moreover is an introductory word and should be followed by a comma.
Incorrect: To become fluent readers students must read outside school hours.
Correct : To become fluent readers, students must read outside school hours.
“To become fluent readers” is an introductory infinitive phrase and should be followed by a comma.
Incorrect: If you want to write well you must be prepared to practice the craft.
Correct : If you want to write well, you must be prepared to practice the craft.
“If you want to write well” is an introductory clause and should be followed by a comma.
2. Nonessential information is set off with commas.
Incorrect: Joseph Conrad who was born in Poland began to learn English in his twenties.
Correct : Joseph Conrad, who was born in Poland, began to learn English in his twenties.
“Who was born in Poland” is a clause that provides nonessential information and should be set off by commas.
3. Essential information does not require commas.
Incorrect: The boys, who vandalized the public gardens, are in police custody.
Correct : The boys who vandalized the public gardens are in police custody.
“Who vandalized the public gardens” is essential information because it identifies which boys are meant. It should not be set off by commas.
4. A comma is placed before a coordinate conjunction that joins two main clauses.
Incorrect: The cougar moved quickly but the tourist reached the safety of the cabin.
Correct : The cougar moved quickly, but the tourist reached the safety of the cabin.
The clauses joined by the conjunction but could stand alone as complete sentences: “The cougar moved quickly” and “The tourist reached the safety of the cabin.” A comma is not needed with a compound verb joined by a coordinate conjunction: “The tourist saw the cougar and ran to the cabin.”
5. A comma is not strong enough to join two main clauses. (Comma splice)
Incorrect: Circumstances required the children to live in a homeless shelter, nevertheless they kept up with their studies.
Correct : Circumstances required the children to live in a homeless shelter; nevertheless, they kept up with their studies.
Also Correct: Circumstances required the children to live in a homeless shelter. Nevertheless, they kept up with their studies.
A comma splice results when two main clauses are joined by a comma. The main clauses here are “Circumstances required the children to live in a homeless shelter” and “nevertheless, they kept up with their studies.” The word nevertheless is a conjunctive adverb. Its function is to provide a transition between two thoughts, but it is not a joining word like and or but. A comma splice can be avoided by placing a semicolon after the first clause or by ending the first clause with a period or other end stop and starting a new sentence with a capital.
6. A comma is not needed before a noun clause in ordinary narration.
Incorrect: The spelunkers found, that the caves were closed to protect the bats.
Correct : The spelunkers found that the caves were closed to protect the bats.
The noun clause is “the caves were closed to protect the bats.” The clause functions as the direct object of the verb in the main clause, found.
7. A comma is needed before a direct quotation.
Incorrect: The wizard said “Pay no attention to that man behind the curtain.”
Correct : The wizard said, “Pay no attention to that man behind the curtain.”
8. Colons should be used after a complete sentence to introduce a word, phrase, clause, list, or quotation.
Incorrect: Her favorite flowers are: daffodils, roses, and pansies.
Correct : She has three favorite flowers: daffodils, roses, and pansies.
“Her favorite flowers are” is a sentence fragment. A complete sentence should precede a colon that introduces a thought that expands on the meaning of the sentence that precedes it.
9. Main clauses that are not part of a compound or complex sentence require an end stop. When a period or other end stop is omitted, the result is a “run-on sentence.”
Incorrect: The rushing waves capsized the boat indifferent gulls wheeled overhead.
Correct : The rushing waves capsized the boat. Indifferent gulls wheeled overhead.
The simplest way to correct a run-on sentence is to put a period at the end of the first clause and capitalize the next one.
10. Multiple exclamation points don’t belong in mature writing.
Incorrect: Before my astonished eyes, the house sank into the tarn!!!!
Correct : Before my astonished eyes, the house sank into the tarn!
On the rare occasions that an exclamation mark is wanted in formal writing, one is sufficient.
Bonus: Quotation marks should not be used for mere emphasis.
Incorrect: Our staff is required to take three “safety” courses every year.
Correct : Our staff is required to take three safety courses every year.
In most contexts, placing quotation marks around a word suggests that the word is being used with a meaning other than the obvious one. Writers who enclose words in quotation marks merely for emphasis risk annoying their readers. No one likes to waste time trying to discern a hidden meaning where there is none.
9 thoughts on “Top 10 Punctuation Mistakes”
In the Correct sentence for #5, should there be a comma after “nevertheless”? If not, why not? Thank you.
Shouldn’t the “correct” sentence in #5 require a comma following “nevertheless”?
A conjunctive adverb connecting two independent clauses in one sentence is preceded by a semicolon and followed by a comma. 
One, and as far as I can think only one, of the examples of incorrect usage can be rendered correct by context: “The boys, who vandalized the public gardens, are in police custody.”
That’s just fine if preceded by something like “My kids are in hot water with the cops again. (The boys, who vandalized the public gardens, are in police custody.)”
Glad to see that last one about using quotes for “mere emphasis” or, as I often see them used, as sneer quotes. In the above example, the writer is sneering at the idea these are actually safety courses.
If you disagree with a term that others are using, either let it pass or deal with it in a separate statement, giving reasons for your belief. Don’t abuse quote marks to sneer.
–Michael W. Perry, co-author of Lily’s Ride
I learned these grammar rules when I was in junior high school (that dates me). My rule of thumb is if I naturally pause, chances are some punctuation needs to be applied there.
More and more I see dashes (of various sorts) used to do the work you say in #8 that the colon should do: be used after a complete sentence to introduce a word, phrase, clause, list, or quotation. Is either acceptable?
On another note, I am curious as to use of the word nor vs. or after a negative. I think nor. Am I wrong?
Neither the dogs, nor the cats, were fed this morning.
Neither the dogs or the cats were fed this morning.
Not convinced by your bonus rule: yes, emphasis quotations can be over-used, but they are a convention that exist in both written and spoken English, and they have a different meaning from other forms of emphasis.
Doug, I’d agree with you.