1. Rule #5
Combining Sentences

2. Coordinating Conjunctions
Conjunctions are words that join words or ideas together.
The most common coordinating conjunctions are and, but, or, yet, so.
An easy way to remember these words is the acronym ABOYS.

3. Usage
When you combine two complete sentences with a coordinating conjunction, there needs to be a comma before the conjunction
Correct Options:
I would rather be watching football than grading papers, but I don’t have a choice.
I would rather be watching football than grading papers but don’t have a choice.