What do you call the comma before and?
The presence or lack of a comma before and or or in a list of three or more items is the subject of much debate. Such a comma is known as a serial comma. For a century it has been part of Oxford University Press style to retain or impose this last comma consistently, to the extent that the convention has also come to be called the Oxford comma. However, the style is also used by many other publishers, both in the UK and elsewhere. Examples of the serial comma are:
mad, bad, and dangerous to know
a thief, a liar, and a murderer
a government of, by, and for the people
The general rule is that one style or the other should be used consistently. However, the last comma can serve to resolve ambiguity, particularly when any of the items are compound terms joined by a conjunction, and it is sometimes helpful to the reader to use an isolated serial comma for clarification even when the convention has not been adopted in the rest of the text. In
cider, real ales, meat and vegetable pies, and sandwiches
the absence of a comma after pies would imply something unintended about the sandwiches. In the next example, it is obvious from the grouping afforded by the commas that the Bishop of Bath and Wells is one person, and the bishops of Bristol, Salisbury, and Winchester are three people:
the bishops of Bath and Wells, Bristol, Salisbury, and Winchester
If the order is reversed to become
the bishops of Winchester, Salisbury, Bristol, and Bath and Wells
then the absence of the comma after Bristol would generate ambiguity: is the link between Bristol and Bath rather than Bath and Wells?
In a list of three or more items, use a comma before a final extension phrase such as etc., and so forth, and the like:
potatoes, swede, carrots, turnips, etc. candles, incense, vestments, and the like
It is important to note that only elements that share a relationship with the introductory material should be linked in this way. In:
the text should be lively, readable, and have touches of humour
only the first two elements fit syntactically with the text should be; the sentence should rather be written:
the text should be lively and readable, and have touches of humour
This text has been adapted from Hart’s Rules
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