Commas are sometimes considered a difficult punctuation mark to use correctly. This is because they have many different uses. These include marking:
- sentence structure
- introductory elements
- lists of adjectives
- non-essential elements.
Sentence structure: independent clauses
To use commas correctly, you need to know about independent and dependent clauses. An independent clause contains a subject and a verb. It can stand alone as a sentence.
- The trees lose their leaves.
- The rains didn't arrive this year.
|1. The trees||lose||their leaves.|
|2. The rains||didn't arrive||this year.|
| subject|| verb|| |
We use a comma when we join two independent clauses to make one compound sentence.
- The wet season rains didn't arrive this year, and the trees in the north lost their leaves.
Note: you do not always need a comma if the clauses are short.
- Kim flew to Darwin but Sascha drove.
Sentence structure: dependent clauses
A dependent clause contains a subject and a verb, but it cannot stand alone. It needs an independent clause to make a sentence.
- Because an El Nino cycle causes drier weather
- Whenever drought occurs
|1. Because||the el nino cycle||causes||drier weather|
|2. Whenever||drought ||occurs|| |
| sub-ordinating conjunction||subject||verb|| |
We can combine dependent and independent clauses to make a complex sentence. We use a comma when we put the dependent clause first.
- The trees lose their leaves whenever drought occurs.
- Whenever drought occurs, the trees lose their leaves.
- The rains didn't arrive this year because the El Nino cycle causes drier weather.
- Because the El Nino cycle causes drier weather,the rains didn't arrive this year.
Introductory and transitional elements
We use a comma to mark an introductory word or phrase or to mark a transition.
- Darwin's population dropped several times in the 20th century, such as the declineafter the WWII bombing.
- In 1974, the population of Darwin was 48,000.
- However, the population declined to 12,000 in 1975.
- Because of Cyclone Tracy, the population declined rapidly.
We use a comma to separate the elements in a list. The elements in the list could be words, phrases or clauses.
- Since 2015, Australia has been hit by category 5 cyclones Niran, Veronica, Marcus, Ernie and Marcia.
- You must prepare your cyclone kit, clear objects from your garden, fill containers with water and put batteries into your radio.
Note: in Australia, we do not usually use a comma before the final and in the list. This is known as the Oxford or serial comma. However, you must consider your readers. If an Oxford comma makes your sentence easier to understand, you should use it. Compare these two sentences:
- We require the support of the landlord, the local government, Family and Community Services and Community and Care.
- We require the support of the landlord, the local government, Family and Community Services, and Community and Care.
The final comma in sentence 2 helps the reader understand the difference between two groups: Family and Community Services and Community and Care.
Lists of adjectives
We use a comma to separate adjectives (descriptive words).
- We must renovate that old, unpainted cottage.
- The lanceolate, petiolate, alternate, waxy green leaves on that mature eucalyptus plant are typical.
If you can put an and between the adjectives, a comma will probably belong there. For instance, you could say: We must renovate that old and unpainted cottage.
We use a comma to mark non-essential or descriptive information. This information could be removed from the sentence and it will still be grammatically correct.
- Dr Wang,a lecturer in the Business school,has published extensively on the subject.
- The report, which the intern had edited, explained the agency’s strategy.
- Introduced pests, such as cane toads, threaten Australian eco-systems.