How we change what others think, feel, believe and do
The comma has many uses, although the simplest way of remembering it is that it inserts a pause into the sentence. This can be deliberately used in unusual places in order to build suspense.
Use the comma to separate out a phrase that may be entirely removed without harming the syntax of the sentence. This may be an aside or
Use commas to separate items in a list (but do not put one before the 'and'). If there are multi-word items in the list, use semicolons as separators.
Beware: too many commas can excessively fragment the sentence. If you have lots of commas, seek either to remove some or break the sentence into more, shorter sentences.
The elephant is large, but friendly. (separating pause)
The elephant, although large, is very friendly. (removable phrase)
The elephant was large, friendly, happy and pink. (list)
Commas allow compound sentences to be built up, adding richness and complexity to language. By separating parts of the sentence, the pause of the comma gives the listener time to process what has gone before. It also sends signals about meaning and can be used to avoid ambiguity.
Asides may also be created with parentheses and dashes. Asides created with commas are not as conspiratorial as with parentheses or as separated as with dashes.
It is possible to write with lots of commas or with very few and still have perfectly correct grammar. Yet too many commas tires the reader, whilst too few can lead to ambiguity and confusion (remember that the reader reads serially, not getting the full meaning until the end of the sentence).