What is a comma?

Question

What is a comma?

Answer

A comma is a punctuation mark (,) which has two primary purposes (though there are a multitude of other rules for its use in different contexts):

1. To separate clauses.
   A clause is a set of words which express a complete idea. For example, ‘I went to France’ is an independent clause (a clause which makes sense on its own and requires no further context). Commas separate dependent and independent clauses; a dependent clause is one which cannot stand alone and needs to be attached to an independent clause to make sense. For example, ‘which I thought was a beautiful country’ is a dependent clause: it does not make sense without understanding which country we are referring to. Putting the two together and separating them with a comma would create the sentence:
   ‘I went to France, which I thought was a beautiful country.’
   The two clauses are closely interrelated, so should not be split with a full stop, but inserting the comma acknowledges that they are separate clauses.
2. To separate items in a list.
   When listing several items, it is important to insert commas to ensure that it is clear what the items are. This can help avoid ambiguity about items in the list. For example:
   ‘I’d like to order fish and chips and steak and chips with peas and gravy and the fish pie and mash and Spaghetti Bolognese please.’
   In this sentence, it is not entirely clear where one item’ (in this context, one meal) ends and another begins. Adding commas in between each item can clarify this by replacing some of the uses of ‘and’:
   ‘I’d like to order fish and chips, steak and chips with peas and gravy, the fish pie and mash, and Spaghetti Bolognese, please.’

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