Commas undoubtedly bring a new source of confusion to essay writing, while, ironically, they are used in order to clarify that which is written. When I began writing university papers, I was completely unsure of my comma use. Do I need one here? And, if so, why do I need one there? Are there places where I do not have commas, but require them?
Most of us are familiar with the use of commas to distinguish objects in a list or in a series: for example, “I went to the store and picked up some tomatoes, cantaloupes, rice and chicken.” Interestingly, the space before the ‘and’ in the above example requires a comma in some styles, but does not require a comma in other styles.
Commas are also used to separate an introductory word or phrase at the beginning of a sentence from the main part of the sentence, the part in which the ‘point’ of the sentence is written. Common introductory words and phrases include however, therefore, also, as a result, etc. An example of how this works is as follows: “As a result, Jonathon will not be able to make it to the basketball game this afternoon.” The introductory element in this case also works as a transition from the previous sentence, as there is some action that has led to Jonathon’s inability to make it to the basketball game this afternoon. Introductory elements in a sentence are, therefore, commonly used as transitions and are usually set off from the rest of the sentence with a comma.
In sentences there is often a main point, or a main clause, as well as a clarifying element, or a non-restrictive element, which reflects on the main point. This non-restrictive element is set off with a comma. For example: “Medical doctors treat many different diseases in humans, helping to keep us healthy.” The main point of the above sentence is that doctors treat many diseases in humans. The non-restrictive element helps to clarify this main statement, that doctors help to keep humans healthy, but it is not essential to the sentence. Non-restrictive/non-essential elements can be placed anywhere in a sentence, not only at the beginning. For example, the same sentence can be reorganized: “Medical doctors, helping to keep us healthy, treat many diseases in humans.”
In many sentences there are two main clauses that are connected by a coordinating conjunction, such as and, but, for, or, so, nor and yet, which are preceded by a comma. In other words, these are sentences with two main points. For example: “The weather is incredibly cold today, and it is raining. The fact that it is cold outside is a main point or clause, and the fact that it is raining outside is also a main point. In other words, both of the points could stand alone as sentences themselves. That is why a coordinating conjunction is used: to connect two clauses that would otherwise constitute separate sentences.
Another common use of the comma is to separate two adjectives that are modifying the same noun. For example: “This cold, foamy glass of beer is good.” In this case the comma is doing the job of the word ‘and’; it is combining two separate adjectives which modify the same object, the glass of beer.
The above explanations and examples are intended to illustrate a few of the most common uses of the comma.