Punctuation is definitely stressed on the ACT and SAT, and comma rules are probably among the most commonly tested. While many rules are just that (a guiding principle), some rules are more ‘guiding’ than ‘principle.’ This is the case with the Oxford, or serial, comma that is optional depending on preference.
The Oxford comma (named for the preferred style of the Oxford University Press) is the last comma that appears in a list. For example,
I went shopping and bought a pen, pencil, and stapler.
The Oxford comma is the last comma in the list (between ‘pencil and the word ‘and’). Many would leave out this comma so that the sentence looks like this:
I went shopping and bought a pen, pencil and stapler.
In this case, it’s clear what the person means. However, there are situations where leaving out the Oxford comma affects the meaning of the sentence. Consider the following sentence:
During my trip to Washington, D.C., I saw two clowns, a Senator, and a Congresswoman.
As written, this sentence describes three separate sightings, one with two people (clowns) and two others involving one person (a senator and Congresswoman). Now let’s examine the sentence without the Oxford comma:
During my trip to Washington, D.C., I saw two clowns, a Senator and a Congresswoman.
The sentence now means that there was one sighting – a Senator and Congresswoman who the author considers clowns! This example clearly supports the use of the Oxford comma to reduce ambiguity. However, many people argue that this kind of ambiguity is easily corrected by rearranging the list, as follows:
During my trip to Washington, D.C., I saw a Senator, a Congresswoman and two clowns.
Now, it becomes pretty obvious that there were three sightings.
So where does this leave us? If you are a careful writer and understand the potential for ambiguity, you can get away with skipping the Oxford comma. However, in situations where ambiguity may arise or if you’re in a hurry–like when writing ACT & SAT essays–it’s probably safer to include that last comma!
Dave Holtzman(https://chariotlearning.com)