Philosophers do not agree about anything to speak of. And why not? How can it be that equally intelligent and well-trained philosophers can disagree about the freedom of the will or nominalism or the covering-law model of scientific explanation when each is aware of all the arguments and distinctions and other relevant considerations that the others are aware of? How can we philosophers possibly regard ourselves as justified in believing anything of philosophical significance under these conditions? How can I believe (as I do) that free will is incompatible with determinism or that unrealized possibilities are not physical objects or that human beings are not four-dimensional things extended in time as well as in space when David Lewis—a philosopher of truly formidable intelligence and insight and ability—rejects these things I believe and is aware of and understands perfectly every argument that I could bring in their defense?

Peter van Inwagen, ‘Quam dilecta’, in Thomas V. Morris (ed.), God and the Philosophers: The Reconciliation of Faith and Reason, New York, 1994, pp. 40-41