Axioms, or First Principles, or what cannot be avoided (by a rational person).
1. There is a way that things are. Or, we can say there is a way that the universe is. This is a fundamental ONTOLOGICAL truth and cannot be denied without self-contradiction.
2. Reason is the ultimate authority, the only authority, actually, for determining what is true about the universe. This cannot be denied without self-contradiction.
3. Opposing truth claims cannot both be true. This cannot be denied without self-contradiction. We generalize to say that all self-contradictory statements are FALSE. In English, we can't have it both ways. We can't have our cake and eat it too.
4. Since there is a material world as well as a world of reason (an immaterial world*) we need something besides reason to determine what is true. We need empirical evidence. Or sense experience. This is not a first principle but it should be apparent to even the biggest skeptic. It's certainly undeniable that physical things exist.
5. Therefore, empirical evidence plus reason = the best truth that we can have about the way things are. (This is essentially the scientific method.) This is a combination of axioms 2 and 4.
6. My (and your) best interests are best served by knowing what is true. This isn't axiomatic but it certainly seems true to me. It may be possible to envision a circumstance where I might be better served by a lie but I'd bet not. In any case, in a general way, I think it is safe to claim that our best interests are served by truth rather than falsehood.
There are more axioms but I have not yet given the rationales so I will add to this list later.
*The next post will be a deconstruction, or destruction, of the ontological position of materialism, or physicalism, or naturalism. Or whatever "ism" you want to call it. The fundamental idea is that all that exists, all that is real, in the universe is matter and energy. Or we may say sub-atomic particles in energy fields.