====== Synderisis ======
The fundamental obligation imposed on us by right reason is to "do good and avoid evil."

This basic principle cannot be derived from any higher principle.

It cannot be "proved" by formal proof based on axioms of logic.  It is something taken for granted in and by logic.  We //ought// to accept the conclusions of logic, where they apply, because this is the good of the mind (to know the difference between what is true and false).  Without the assumption of synderisis, logical reasoning has no force.

Those who deny that we //ought// to do good and avoid evil can form their denial only by appealing to it.  They say, "You //ought not// to believe that people //ought// to do good and avoid evil; it is evil (wrong) for you to hold that view."  This is a self-referentially inconsistent position; it is a form of hypocrisy to say one thing ("People cannot be obliged to do good and avoid evil") and do another (describe a standard by which the listener is obliged to do good and avoid evil).