Rules for using commas and semicolons have been debated for years, and there are a number of sources that offer an opinion on how to use them. However, there are a few simple or basic guidelines that work most of the time.
Commas with a series of items
Simple list—Use commas to separate each item, except the last one.
– A string of words connected by and—”The fabric was in four colors: red and blue and green and yellow.” To avoid the repeating and so many times, especially in a long list, a comma replaces each conjunction (and). This yields: “The fabric was in four colors: red, blue, green and yellow.” However, there are occasions when the last two words might, themselves, be conjoined as a single term. To avoid possible confusion, common formal practice places a (redundant) comma before the conjunction and. Thus, the sentence would be written as: “The fabric was in four colors: red, blue, green, and yellow.” (If read literally, this would be: “The fabric was in four colors: red and blue and green and and yellow.”)
– A string of words connected by or —The same rule applies to a strong of words connected by the conjunction or. Substitute or for the conjunction and above.
List of multiple-word phrases—For clarity, use a comma before the last conjunction (eg, New York City, Philadelphia, Chicago, and/or San Francisco)
List with complex elements that might each include one or more commas—Use a semicolon instead of a comma to separate the list items. Example: I have lived in several large cities including Atlanta, Georgia; Kansas City, Missouri; and Portland, Oregon.
A corollary of this rule is that a comma should be placed both before and after the state name in a sentence (eg, I lived in Baton Rouge, Louisiana, for three years). This is true even if an abbreviated form of the state name is used (eg, I lived in Baton Rouge, LA, for three years).
The same rule applies to dates (eg, I moved to Los Angeles on June 23, 1996, soon after I graduated). Notice that both sides of the year have a comma. However, there should be no comma when the following date forms are used: 23 June 1996 or June 1996.
Before-and-after commas should also be used in direct address (eg, “You know, Mary, you should be more careful.”). Likewise with titles (eg, Robert Smith, PhD, was the guest speaker)
Multiple adjectives modifying the same noun—This is one of the more confusing issues. The general rule here is relatively easy to remember: Use a comma to separate the adjectives when the word and could correctly be inserted between them. For example, an expensive ski lodge is correct (one would not say an expensive and ski lodge). However, in spite of the rule, it’s okay to write long red hair, rather than long, red hair. If the list of modifying adjectives gets long, commas are probably appropriate (eg, the hot, dry, baking, scorching desert). A comma also avoids confusion in the following sentence: To John, Worthington was something of a dreamer.
Commas to separate independent phrases or thoughts
Use a comma to isolate separate or independent phrases or thoughts (like mini-sentences) within a sentence. These are often indicated by the use of a conjunction (words like and, or, nor, but, yet, so, for). Be careful here. The following sentence [modified to protect the writer’s copyright] is an example: They saw the airplane and they ducked. The word and makes one think ahead that there’s a list coming (eg, They saw the airplane and the helicopter), but in this case, what’s coming is another thought (they ducked). These two thoughts should be separated by a comma ([First] they saw the airplane, and [then] they ducked). Other examples: I like gardening, and I also enjoy playing golf. She got off work early, so she decided to take a short hike.
This applies to introductory phrases (ie, before the main thought of the sentence). The simple rule is: Use a comma between the introductory phrase and the main clause if it refers to a
– cause/purpose/reason/result (eg, because, in as much as, in order (to, that), in so far as, since)
– concession/comparison/manner (eg, although, as/even (though), just as, though, while)
– condition (eg, as/even if, if, unless, whether)
– place (eg, where, wherever) or
– time (eg, after, as (far/soon/long) as), before, now that, once, since, until, when, whenever, while).
Examples: If I could drive, I’d really go places. To win the game, the team put out exceptional effort. Whenever the wind blows from the south, we get rain.
When the independent phrase is in the middle or end of the sentence, there are two conditions:
1) if the phrase is needed by the sentence, no commas should be used to separate it from the main thought
2) if the phrase is not needed by the sentence, commas should be used to separate it from the main thought.
Examples: I’d really go places if I could drive. We get rain whenever the wind blows from the south. He was always liked, wherever he went. John, on the other hand, seemed to be universally distrusted. Our people, being a minority of the voters, never seem to put a candidate of our choice into office.
Comma to introduce a quote
Use a comma (or a colon) to introduce a quote (eg, When asked about the weather, Jane always said, “Whatever,” and people knew not to push further). Notice that the comma (or a period) goes inside the quotation mark. This is usually true. The only exception might be when quotation marks surround a phrase (eg, He preferred the phrase “Get ahead”, rather than the phrase “Go for it”.). However, it would be just as correct to write this as He preferred the phrase “Get ahead,” rather than the phrase “Go for it.”
Commas in all other situations
a) Use a comma only when necessary (for clarity, for example); b) Always use a comma to avoid confusion (eg, I prefer yellow and blue, and green is my wife’s preference); c) A comma should be inserted wherever a speaker would normally take a break or a breath. Here are some examples: Later on, he became a writer. Even though Bob was stronger, Jane prevailed. Entirely on her own, Betty became an accomplished musician. Bob was tall, Sarah was short, but they made a handsome couple.
One way to think of the common punctuation marks is like the buttons on a recording device: a comma is like the Pause button (a short stop), a period is like the Stop button (a full stop), a semicolon is like a brief Pause and Continue, and a colon is like a long Pause and Continue.
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