In the Summa Theologica, shortly after arguing for the existence of God, Saint Thomas Aquinas writes the following: “Having recognised that a certain thing exists, we have still to investigate the way in which it exists, that we may come to understand what it is that exists.” This seems like a peculiar thing to state. I know that there exists something, but I have no idea as to what this thing is. As Brian Davies points out in his book Philosophy of Religion: A Guide and Anthology, this not such an odd statement after all. Suppose I attempt to open a door, and something stops it from opening. I might say, ‘well something is certainly in the way’. If it makes sense to make this statement, it also makes sense to ask, 'what is it'?