Isaac Newton was one of the greatest physicists of all time. (After all,) he was the discoverer of the law of gravity.
My answer: in the parenthesis is a premise indicator
Actually, "after all" is not a premise indicator, but rather a discourse marker used to emphasize or provide additional information. It doesn't necessarily indicate a premise in the logical sense.
To accurately categorize "after all" as a premise indicator, it's important to understand what a premise is in logic. In logic, a premise is a proposition or statement that supports or provides evidence for a conclusion. It's often used in the context of deductive reasoning to build an argument.
If we were to rephrase your statement to include a premise, it could be something like this:
"Isaac Newton was one of the greatest physicists of all time because he was the discoverer of the law of gravity."
In this case, "because" would be a more appropriate premise indicator since it introduces a reason or evidence for the claim that Newton was one of the greatest physicists.