It's tempting to call the Principle good and the Antithesis evil. However, instead the game uses its own internal moral compass of principled vs. antithetical ideas. This moral compass is loosely defined by morality in real life, but the details are defined by the gods and their players.
What is "principled" is defined as being aligned morally with the Principle, and what is "antithetical" is defined as being aligned morally with the Antithesis. While the Princes are largely principled beings, they are also imperfect, and so do have minorly antithetical natures. Similarly, the Adversaries are largely antithetical beings, but have minorly principled natures.
Each Prince is an incomplete reflection of different facets of the Principle, as opposed to perfect reflections of the Principle as a whole. Morality is by its nature very complicated and context-sensitive, and this is no less true for the Principle than it is in real life. Thus, it follows that each Prince would naturally have their own take on what is and isn't principled.