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Grammar and Punctuation


Comma usage is, in some respects, a question of personal writing style. Some writers use commas liberally, while others prefer to use them sparingly. Most modern North American style guides now recommend using fewer commas rather than more. Therefore, when faced with the option of using a comma or not, you may find it wise to refrain (Peck, 2011).

This course will outline the key elements of how to use commas, and then allow you to test your knowledge using the educational tools provided.

comma splice is an error caused by joining two independent clauses with only a comma instead of separating the clauses with a conjunction, a semicolon, or a period. A run-on sentence, which is also incorrect, is created by joining two independent clauses without any punctuation.

Time flies when we are having fun, we are always having fun. (Comma splice)
Time flies when we are having fun we are always having fun. (Run-on sentence)

Time flies when we are having fun; we are always having fun.
Time flies when we are having fun, and we are always having fun. (Comma is optional because both strong clauses are short.)
Time flies when we are having fun. We are always having fun

Separating Items in a List

Most authorities on English, including the American Psychological Association, the Modern Language Association, and The Chicago Manual of Style recommend the use of the serial comma (see below). Use of the serial comma may add ambiguity or provide clarity depending on the situation. With that in mind, many sources also suggest neither systematically using nor systematically avoiding the use of the serial comma.

Example: My remaining assets are to be split among my wife, son, brother, and sister. 
 *Omitting the comma after brother would indicate that the brother and sister would have to split one-third of the estate

MLA Style Manual and Guide to Scholarly Publishing (2009) 3.2.2. Commas (p. 67)

American Psychological Association (2010) 4.03 Comma (p. 88)

The Chicago Manual of Style (2010) 6.19 Serial Commas (p. 312)

Practice using commas in a list of nouns, verbs, and adjectives

After introductory phrases or clauses

Use a comma when a sentence begins with an introductory infinitive clause, prepositional clause, participial clause, or subordinating clause. 

*There is always an independent clause (or complete sentence) following any type of introductory clause

Use a comma after introductory infinitive clauses.

Example: To improve her English, she read for an hour before bed each night.

Use a comma after introductory prepositional clauses.

Example: Before he went to New York, he had spent a year in Australia.

Use a comma after introductory participle clauses.

Example: Having said this, he left the room.

Use a comma when a subordinating clause is used to begin a sentence. Common subornating conjuctions include; although, unless, before, whenever, as long as.

Example: Whenever I'm on a road trip, I always keep a close eye on my fuel level.

Surrounding non-essential words, phrases, or clauses

Use a pair of commas in the middle of a sentence to set off clauses, phrases, and words that are not essential to the meaning of the sentence. Use one comma before to indicate the beginning of the non-essential and one at the end to indicate the end of the non-essential.

Here are some clues to help you decide whether the sentence element is essential. If you answer yes to one or more of these questions, then the element in question is nonessential and should be set off with commas

  • If you leave out the clause, phrase, or word, does the sentence still make sense?
  • Does the clause, phrase, or word interrupt the flow of words in the original sentence?
  • If you move the element to a different position in the sentence, does the sentence still make sense?

Example of a non-essential word: I know Bill and Steve are out of work right now. I will,therefore, offer to pay for supper and drinks.

Example of a non-essential phrase: All the snowfall created great skiing conditions. The visibility, on the other hand, was terrible.

Example of a non-essential clause: Mr. Macleod, who teaches science to fourth graders, won a nobel peace prize for phsyiology and medicine.

Before coordinating conjunctions

When using a coordinating conjunction (and, but, or, etc.) to link two independent clauses and make a compound sentence, place the comma before the conjunction.

Example: We spent all day at the river fishing, but we didn’t catch anything.

Example: I think I'll have the apple pie, or maybe I'll get the chocolate cake instead.

Five suggested uses of the semicolon

  1. For combining independent clauses that are joined by a coordinating conjunction when at least one of the clauses is long or contains commas.

    • e.g. the dam broke; the area was flooded.

    • The sun had set; lights came on in all the houses.

  2. Use a semicolon to separate two independent clauses that are joined by coordinating conjunction when at least one of the clauses is long or contains commas.

    • e.g. He overhauled the engine, repaired the dent, and replaced the tires; and when he had finished, he sold the car. 

  3. Use as semicolon to separate units of a series when the units themselves contain commas. 

    • e.g. Maud, the violinist; Herber, the flutist; and Grace, the noted harpist, were waiting for their instruments to arrive. 

    • e.g. Several teams received yellow cards during the World Cup series including Germany, 2; England, 1; and Italy, 3.

  4. A semicolon is used to signal the approach of words that explain or specify. Some of these words are as, for example, for instance, namely, that is, that is to say, etc. 

    • e.g. There are several factors that contribute to obesity; namely, poor diet, lack of exercise, and portion sizes.

    • e.g. Some colours blend together very well; for example, brown and yellow.

  5. Use a semicolon to separate two independent clauses that are joined by transition words: besides, for example, for instance, accordingly, therefore, otherwise, consequently, however, instead, hence, etc. Generally a comma follows the transition word.

    • e.g. This book contains two tables of contents; however, only one is alphabetically arranged.

    • Children are basically honest people; therefore, it is unfortunate when adults teach them, by example, to lie. 

When should I be using a colon? 

Colons can be used to join two independent clauses when you wish to emphasize the second clause.

e.g. I forgot my umbrella: we got soaked

Colons can be used to introduce a clause that reflects something in the clause preceding the colon.

e.g. We like several types of movies: the romance is great and the action keeps me awake

Colons can be used to introduce lists, quotations, and explanations.

e.g. I have many different favourite teams: the Oilers, the Flames, and the Blue Jays

e.g. The President of the United States, George Washington, once said: "To be prepared for war is one of the most effectual means of preserving peace".

e.g. This is how it happened: I had a quarter for the meter, then I dropped it down the sewer crack, I come out of the store and BAM I have a parking ticket. 

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