A comma is used:
- after an introductory phrase or clause
Recently, new methods have been developed …
To ensure that the bottle is properly sealed, tip it upside down.
However, the results were inconclusive.
- after every item in a run-on list of more than 2 items (except after the second-last item, which is followed by and, unless a comma is also needed to ensure clarity); if other commas are needed within items, use semicolons between the items
Samples of fruit, cheese, meat, seafood and vegetables were analysed.
Tissue sections were stained with toluidine blue, periodic acid–Schiff stain, and haematoxylin and eosin.
The level of heavy metals was assayed in farm, garden and commercial soils; beach and river sand; and mine diggings.
Hot, sunny, dry weather is typical of summer in Canberra. [The 3 adjectives are all descriptive.]
Many graduates have strong analytical skills. [The 2 adjectives are of different types – ‘strong’ is evaluative, and ‘analytical’ is categorial.]
The presenter had a clear, confident speaking style. [‘Clear’ and ‘confident’ are evaluative; ‘speaking’ is categorial.]
- to set apart a nondefining clause or phrase within a sentence (see also That and which)
The new oven, which we bought last week, has been delivered.
John Smith from Brisbane, Queensland, attended the workshop.
- to set off qualifying clauses or phrases that represent a break in the continuity of thought (dashes or parentheses can also be used for this)
The movie was not as funny as we expected, although we still enjoyed it.
- in numbers of 4 digits or more
1,000 20,500
- to indicate the position of locants in chemical formulae
1,3-dimethyl-2-phenylnaphthalene
- in some other specialised scientific terminology (eg some chromosome and gene terminology).
Tip. To decide whether adjectives should have commas between them, try changing their order or inserting and between them. If the phrase still sounds ‘right’, the adjectives are likely to be of the same type and should be separated by commas.
Do not use a comma:
All the researchers who were at the conference received a prize.
26 February 2013 Tuesday 26 February 2013
In lists ending with etc, use a comma as follows:
We analysed food samples (fruit, cheese, meat, seafood, vegetables, etc).
Use etc sparingly, preferably only within parentheses. Do not use eg to begin a list that ends with etc – this is redundant.
Did you know? A serial comma is a comma placed immediately before the and or or in a series of 3 or more terms (eg We ate fruit, cheese, and bread). The serial comma is sometimes called the Oxford comma because its use is recommended by the Oxford style manual (of Oxford University Press). It is very commonly used in American English (both scientific and nonscientific), but is rarely used in British or Australian English.
In this manual, to maintain consistency with general Australian style and to follow the trend of minimising punctuation, we recommend omitting the serial comma unless it is needed for clarity. Examples where it might be needed are:
- a list of items where some of the items include and (eg We ate fruit, cheese, and bread and jam)
- a list of more complex items (eg The distance from town, contamination of the water with algae, and personnel problems were some of the difficulties the project faced)
- a sentence containing appositive nouns (eg I spoke to my supervisors, the head of the department, and a geologist – however, note that even inclusion of the serial comma does not remove the ambiguity about whether my supervisor is the head of the department or a different person, and a better option would be to recast the sentence).
