Reason alone cannot give definitive answers to questions about what is real. Reason drives us to seek as many explanations of the world as we can, but when it comes to really ultimate explanations, it seems to arrive at a set of incompatible alternative possibilities, between which it is unable definitively to decide. For example, reason cannot decide whether everything is necessarily what it is (the thesis of determinism, espoused by Spinoza), or whether some things are contingent and could logically have been otherwise (Leibniz’s preferred alternative). It cannot decide whether humans have free will, or what exactly it would mean for them to have it. It cannot decide whether consciousness is the ultimate reality or not (all the Rationalists agreed that it is). It cannot decide whether ultimate Mind, if there is one, has revealed anything reliably or not. It cannot decide whether the universe is finite or infinite. And it cannot even decide whether the universe is objectively rational or a product of chance, ‘born of night’, in Aristotle’s phrase… That does not mean that reason is useless. It means that reason alone cannot definitively resolve ultimate questions about human and cosmic being.
– Keith Ward, God and the Philosophers