Academic Language and Learning
A guide to using Commas
Student A: “If a sentence is too long I put in commas to break it up.”
Student B: “Commas go in where you pause for breath, don’t they?”
Student C: “It doesn’t really matter if I don’t use commas correctly, does it? The meaning of my sentences is still clear.”
Although these responses to the use of commas are common, none is correct. In general, punctuation proceeds by carefully defined rules, not by chance, length of sentence, or even breathlessness, and commas can make a difference to meaning.
For example:
I told them to eat, Lucy.
I told them to eat Lucy.
The difference in punctuation is small, but the difference to Lucy is considerable. Incorrect comma use can make a sentence ambiguous or unclear. Look at the following examples.
- Relative clauses
Scientists, who conduct important research, are well respected in the community.
Scientists who conduct important research are well respected in the community.
The first sentence refers to all scientists, and assumes that they all conduct important research.
The second sentence is stating that those scientists who conduct important research are respected by the community. This does not necessarily include all scientists.
Sentences containing words like who, that or which sometimes require a comma and sometimes do not. It depends on the meaning which you are trying to convey.
- Dependent and independent clauses
*When we finally packed up the instrument had already completed the analysis.
When we finally packed up, the instrument had already completed the analysis.
The first sentence is difficult to read because it may seem like the instrument was packed up.
In the second sentence, the comma after the first clause makes the meaning much clearer.
- Coordinating conjunctions in compound sentences
*There isn’t enough time and money is always difficult to find.
There isn’t enough time, and money is always difficult to find.
The first sentence is difficult to read because the word enough appears to apply to both time and money. Using a comma before a conjunction (a word like and, so or but) will separate the clauses and will keep the meaning of the sentence clear.
- After adverbials
*In the lab reports were made about students altering data to fit the hypotheses of the experiment.
In the lab, reports were made about students altering data to fit the hypotheses of the experiment.
The first sentence is difficult to read and its meaning is not clear because the words lab and reports are often used together as a compound noun.
In the second example, a comma separates “in the lab” from “reports” (a verb) and so makes the meaning of the sentence clear.
- Non-tensed verb
*The reagent was added to the solution quickly causing a slow reaction to occur.
The reagent was added to the solution quickly, causing a slow reaction to occur.
Without the comma in the first sentence, it is unclear whether the word quickly refers to how the reagent was “added to the solution”, or the speed at which it caused “a slow reaction to occur”.
Logically, the word quickly can't refer to the second half of the sentence because “quickly causing a slow reaction to occur” does not make sense.
The comma helps to avoid confusion here.
- Lists
The actress sued her neighbour, an archbishop and a truly moral man.
The actress sued her neighbour, an archbishop, and a truly moral man.
In the first sentence, the actress is suing only one person; in the second, writs are flying everywhere!
Always make sure that, when you write a list, the commas are placed to make your meaning clear and unambiguous.
Some other comma rules
Use a comma after “lead in” words or phrases -
However,
Therefore,
Consequently,
As a result,
In fact,
In the laboratory,
At the beginning of each semester,
When these words and phrases are used in the middle of a sentence, they should be enclosed in commas. For example: Many researchers have, in fact, taken this into consideration.
Do NOT use a comma to join two short sentences. Use a conjunction!
Example:
*The benefits of this kind of therapy are substantial, there are relatively few adverse side effects. INCORRECT
The benefits of this kind of therapy are substantial, and there are relatively few adverse side effects. CORRECT
(This is called a comma splice error. Microsoft Word grammar check will often give you a green squiggly line under the word before the comma and will suggest using a semicolon instead of a comma. However, this is not always a good suggestion because semicolon usage is quite specific (See SEMICOLONS). It is often better to join the two sentences with a conjunction such as and, so or but.)
Do not use a comma after the subject of a sentence
Example:
*Recent studies on the mating behaviour of the endangered three toed sloth from South America, have analysed the frequency of the ‘ay-ay’ mating call. INCORRECT
Recent studies on the mating behaviour of the endangered three toed sloth from South America have analysed the frequency of the ‘ay-ay’ mating call. CORRECT
When the subject of a sentence is very long, you may feel that you need to put a comma between the subject and the verb. This is never correct.
For more information about subjects and verbs in sentences:
http://www.unc.edu/depts/wcweb/handouts/commas.html
|
