A journey needs two fundamental pieces of information to be successful: a destination (telos) and a route. In the case of philosophy, the destination is wisdom or truth, with happiness being a by-product. The route is harder to determine. Many famous thinkers since the first philosopher, Thales, have used different paths and arrived at different outcomes. I use four Catholic guideposts when evaluating a proposed philosophical system to determine if it has the correct route and destination.
Guideposts are not axioms, obvious truths that must be taken as true for a starting point. Thomas Aquinas in his famous Five Ways to prove the existence of God started one with the contingency of being. We know by experience that some things come into existence, and that some things go out of existence – life and death. This is an axiom.
Guideposts are not syllogisms. Syllogisms are a form of logic that employs deductive reasoning using sound premises that lead to a conclusion. A common example of a syllogism is: All men are mortal. Socrates is a man. Therefore, Socrates is mortal.
Rather, guideposts help one to navigate a sound path when the route becomes confused and treacherous. Guideposts indicate or sign one to a proper course of acting. These indications can help one to discern good or bad philosophy. Good philosophy leads to beatitude. Bad philosophy leads to dangerous consequences both for the individual and society. It takes little effort to recall the disaster of Marxism and the over 100 million people (and counting) who have died as a result of that failed way of thinking.
The question of why four comes to mind. I like simplicity of approach in a difficult endeavor. There could very well be more than four signs but I have found these four a very good place to begin. Guideposts are a limiting proposition not a maximal one. All four must be present to have a sound catholic philosophy, not only one. If one of the signs is missing, the error is identified, then I determine if it is worth fixing, then move on. Whether it is Thales, Aristotle, William of Ockham, or Thomas Nagel I have found these guideposts extremely helpful in discerning the proposed thinking.