The proposition that the existence of God is demonstrable by rational argument is doubted by nearly all philosophical opinion today and is thought by most Christian theologians to be incompatible with Christian faith. This book argues that, on the contrary, there are reasons of faith why in principle the existence of God should be thought rationally demonstrable and that it is worthwhile revisiting the theology of Thomas Aquinas to see why this is so. The book further suggests that philosophical objections to proofs of God’s existence rely upon an attenuated and impoverished conception of reason which theologians of all monotheistic traditions might wish to reject. Denys Turner proposes that on a broader and deeper conception of it, human rationality is open to the ‘sacramental shape’ of creation as such and in its exercise of rational proof of God it in some way participates in that sacramentality of all things.