From Hans Morgenthau’s classic text on international relations, Politics among Nations: The Struggle for Power and Peace:
The theory, in other words, must be judged not by some preconceived abstract principle or concept unrelated to reality, but by its purpose: to bring order and meaning to a mass of phenomena which without it would remain disconnected and unintelligible. It must meet a dual test, an empirical and a logical one: Do the facts as they actually are lend themselves to the interpretation the theory has put upon them, and do the conclusions at which the theory arrives follow with logical necessity from its premises? In short, is the theory consistent with the facts and within itself?
Here are a few posts I’ve done on theories, models, and evidence: