As a university lecturer of English one of the subjects I teach is basic composition. I do not teach grammar, but grammar and syntax often make out part of essay writing. It is inevitable. One thing that the American style textbooks we use advocate is not having a comma before the final “and” in a list. This comma is sometimes referred to as the “serial comma.” In the following example we see how American English neglect the final serial comma: “I like apples, bananas, lemons and gooseberries.” In British English the comma is required: “I like apples, bananas, lemons, and gooseberries.” This is known as the Oxford comma.
Some people would probably say that it doesn't matter and that it is merely a question of geographic preference, such as the pronunciation of tomato as either to-may-to or to-mah-to. While I'm usually fairly flexible with language, I think the extra comma just before “and” serves a very important purpose and leaving it out can causes confusion, especially when the list contains combined items. For example: “I like apples, bananas, lemons, and gooseberries and blueberries.” Notice how the meaning and feel of this sentence changes when we remove the final comma: “I like apples, bananas, lemons and gooseberries and blueberries.” Without the final comma in the latter sentence, lemons, gooseberries, and blueberries are combined as one syntactical unit, which differs from the former sentence where “lemons” is differentiated from the two berries; with “gooseberries and blueberries” forming one syntactical unit and “lemons” forming a separate syntactical unit, like “apples” or “bananas.”
For a while now I've omitted the final comma in much of my writing in an attempt to practice what I preach (or rather to practice what the textbooks from which I teach preach). However, having thought about it for some time, I am resuming the British custom as it communicates meaning better in my opinion, as illustrated above. Now, I'm not saying that one ought never leave out the final serial comma. There may be poetic value in its exclusion. Commas not only separate items, they also indicate a natural pause in language and the writer (poet) may wish to leave out that comma for the sake of rhythm or tempo.
