Christian philosophy is also interwoven with religious and theological themes: it can’t indeed separate itself from the so-called “revealed truths,” and therefore from the faith, and it has its true subject in God, within whom exclusively the world and the self can be understood, as the creature is understood in the creator, the finite in the infinite. Hence the different positions on the duties and the limits of philosophy, but always within the premise of its symbiosis with the contents of the revelation.
Augustine talks about the unity of faith and reason and of their necessary complementarity. Faith is the prerequisite to rational examination: you need to believe in order to understand, and even rational examination, the act of knowing, answers to God’s command. From this perspective, knowledge itself is not a simple logical exercise, but it is the search of truth made possible by constant divine assistance that “illuminates” the human mind. Hence the lack of distinction between philosophy and reflection on the dogmas of faith: the intellect continues and enhances the first and fundamental religious experience and pulls towards the beatific vision which will be the full contemplation of truth (that is God).
Medieval speculation followed this mentality before the rediscovery of Aristotelian philosophy, which radically changes the context of medieval philosophy. It is at this point that we find the definition of natural philosophy and reason, extraneous in their nature to Christian tradition and reason, and the problem of their relationship to theology, that is to Christian speculation, arises. Thomas Aquinas will make the most notable and coherent effort of welcoming Aristotle’s philosophy within theological speculation, after distinguishing the two.
The reason is autonomous and it can ascend from tangible reality to higher forms of reality, up to the existence of God, which it can prove, as it can prove some of its attributes. Beyond reason, there are some unprovable truths such as the Trinity, the creation in time, the incarnation, the original sin. But the fact that they lie beyond reason does not mean they are irrational: instead, reason has the function of preparing us to accept these truths, because they do not go against reason, compared to which they are instead probable (or non-contradictory).