You don’t always need a comma when using “and”

While recently editing a research proposal I was reminded of a comma error I frequently find myself correcting: always preceding “and” with a comma.

Here was the example sentence:

When I finish this research I will report to the post-secondary community, as well as the class members, and Dr. Smith.

Preceding “and” with a comma is reserved for 2 occasions:

1. if “and” joins more than 2 items in a series (although there is debate about whether this is even necessary)
2. If “and” is a coordinating conjunction joining to independent clauses

To illustrate:

1. I bought jalapeños, habaneros, and scotch bonnets.
2. I went to the store, and I bought runners.

One could rewrite the above example sentence to include a series and make the comma legitimate:

When I finish this research I will report to the post-secondary community, the class members, and Dr. Smith.

Or you could just remove the comma.

Here’s an errant comma from a master’s thesis of a different client and used slightly differently:

This work is a valuable addition to the existing non-scholarly accounts of the team, and provides a critical lens through which the mythologized championship teams may be viewed.

Because “and” joins one independent clause and one dependent clause, there is no need to use the comma. Including the comma implies that the second clause can stand on its own, but it has no subject.

If you want to keep the comma, just add a subject to the second clause to make it independent:

This work is a valuable addition to the existing non-scholarly accounts of the team, and it provides a critical lens through which the mythologized championship teams may be viewed.

Or you could just remove the comma.

I come across inerrant commas preceding “and” so often that I wonder whether people have been taught at some point to always include a comma when using “and”. It’s just not true. Just with a list of 3 or more items and when joining 2 independent thoughts.