meaning - premise or principle? which one?

these words almost bear the same meaning I assume, but not sure if they are exactly the same.. if not, when is it better to use each?

Answer

A premise is a statement that you assume is true for the purpose of doing something else, such as constructing an argument or planning a course of action. A premise can be either a factual assertion ("The sky is blue") or a subjective statement or opinion ("The Beatles were the greatest band of all time").

A premise is a kind of shortcut that lets you avoid doing extra work and concentrate on the task that's in front of you: if you take as a premise that the sky is blue, you can act on that without having to prove that the sky is blue. Of course, it's possible for a premise to be factually incorrect. If your premise is that the sky is green, and you take actions or construct arguments that assume the sky is green, you're going to run into trouble.

A principle, in the sense that you mean, is a doctrine or belief that serves as the basis for a system of belief or action. It's similar to a premise, but is more general. To understand the difference, consider the first line of the Gettysburg Address:

Four score and seven years ago, our fathers brought forth on this continent a new nation, conceived in liberty and dedicated to the proposition that all men are created equal.

"All men are created equal" is both a principle and a premise. As a principle, it's a general statement of belief: if you believe in the principle that all men are created equal, that can affect what else you believe in and how you live your life. The founders of the United States took this principle as a premise when creating and developing the US government and system of laws.