How Can Principles Be Verified?
Principles are drawn logically and they are verified for their being logical and consistent. By comparing two different principles can tell which one is more logical or plausible than the other.
To be honest with you, you should read the work of Nietzsche. I suggest you begin with “Beyond Good And Evil” and “Human, all too Human”. So you can get to a place where there’s no truth or falsehood, no good or evil, no supernatural “beyond human” foundation, whether it be religion or philosophy. A place human, all too human. If you are looking for certainty and spiritual comfort, you can ignore my answer as incoherent rambling. As for human nature, fitrah. It’s an empty slogan. Didn’t Bulleh Shah say “Bullah Ki jaana mai kaun”. I truly don’t know myself so l am skeptical of the claim to know oneself, let alone the claim to know every human being’s nature, if it even exists in the first place as something static and to be found, not as something subject to change by known, unknown, internal and external forces.