Commas are also used for independent clauses that ... are separated by a [coordinating] conjunction
(for, and, nor, but, or, yet, so):
The project was tedious, but the district supervisor said it was vital.https://owl.purdue.edu/owl/english_as_a_secon...Chapter 6 in [t]he
Chicago Manual of Style(
https://www.chicagomanualofstyle.org/book/ed1... )
lays out the rules for conventional comma usage ...
A comma is normally placed before a coordinating conjunction
(and, but, or, so, yet) that joins two independent subject-verb clauses—that is, clauses that could stand on their own as complete sentences.
I kept a composition book on my writing desk, but its pages remained blank. ...
... each edition of
The Elements of Style dating back to the very first (privately printed for William Strunk Jr. in 1918, long before it became Strunk & White) recommends this comma, and it has been explicitly recommended by Chicago since the 11th edition of the
Manual (in 1949). In the 17th edition, the rule is stated in paragraph 6.22.
(
https://www.chicagomanualofstyle.org/book/ed1... )
http://cmosshoptalk.com/2019/06/18/commas-and...A comma is used between two independent clauses joined with a coordinating conjunction.
https://eliteediting.com/resources/chicago-ma...Here is something from an authoritative source,
The Chicago Manual of Style Guide, 17th ed. ... :
When independent clauses are joined by
and, but, or, so, yet, or any other coordinating conjunction, a comma usually precedes the conjunction.
If the clauses are very short and closely connected, the comma may be omitted (as in the last two examples) unless the clauses are part of a series.
https://ell.stackexchange.com/questions/23396...
