After having provided what he takes to be valid proofs of God’s existence, St Thomas Aquinas takes what is, to modern eyes, a surprising turn. At the start of the third question of the Summa Theologiae, Thomas observes that usually when we have shown that something exists we can go on to ask what that thing is – we’ve discovered the Higgs Boson; great that’s a subatomic particle of a particular sort, it fits into our best physical theories in particular ways, and we can do some more science to find out more about it! But things are not like this with God, thinks Thomas, we cannot know what God is, only what God is not.