We rule by love, not by force.
4. Between two independent clauses connected by a conjunction.
The press was out of order, but we managed to start it.
5. Before a conjunction when the word which preceded it is qualified by an expression which does not qualify the word which follows the conjunction.
He quickly looked up, and spoke.
6. Between relative clauses which explain the antecedent, or which introduce a new thought.
The type, which was badly worn, was not fit for the job.
If the relative clause limits the meaning of the antecedent, but does not explain it and does not add a new thought, the comma is not used.
He did only that which he was told to do.
7. To separate parenthetical or intermediate expressions from the context.