My philosophy is founded upon two self proving principles. Principles that to refute presuppose the principles.
The first is the law of non contradiction. A proposition is either true or not true. To refute this principle presuppose that it is either true or not true. Indeed, the principle is the very idea of refutation, and so quite rightly cannot be refuted.
To base decisions on this principle however does not seem to lead directly to any particular way of life. It can identify certain sets of actions as inadmissible, but does not seem to resolve any particular action in itself. It will simply tell us that one cannot both eat to sustain oneself and take a daily dose of poison to kill oneself. These actions together are unreasonable. Taken apart however, it is less easy to discern.
Fortunately, there is only one other consistent self justified principle one can assume. The assumption of all contradictories to this principle leads to a contradiction. And so the second principle is derived from the first principle.
The second principle is the search for truth. To refute the idea that one is searching for truth presupposes having searched for the truth of the matter. Since one can never say “one should not search for truth†, for saying such contends that it is a true principle one can discover, given two courses of action, one must always take the one that leads to the most truth, lest one live in contradiction with the first principle: that one should not contradict oneself.
The skeptic may claim that one cannot know that one decision leads to more truth than another. First, the skeptic is claiming this is true, and so contradicts their own proposition that truth cannot be found.
Second, for any given action the proposition “this action shall lead to the most truth†is by the law of non-contradiction either true or not true. How to practically figure out which actions lead to more truth than other actions, is of course a truth one would have to search for.
The first principle is also derivable from the second, as to conclude that the law of non contradiction is true is to presuppose one is searching for truth, and to claim that this was a valuable discovery is to presuppose that one should be searching for truth.
Thus, these two mutually self justifying principles form a complete foundation for action.