Aquinas holds a version of the causal principle, that things which cannot of their essence fully account for their existence require an outside cause to exist. Chapter 3 goes further into Aquinas’s views on causation and issues surrounding accounting for why things exist. The discussion uses as a point of departure the classic question, “Why is there something rather than nothing?” The chapter looks at various approaches to, and critiques of, the question. This includes the views of Leibniz and also those of Bertrand Russell and Fredrick Copleston in their famous radio debate in 1948 on the existence of God. There is then a look at David Hume’s serious challenge to the view that whatever begins to exist must have a cause. The chapter then turns to how quantum scientific developments in the twentieth century are seen to pose problems for the causal principle. Might quantum considerations offer a universe from nothing? A last section looks at whether there are philosophical considerations positively supporting the causal principle.

Chapter 2 covers elements in Aquinas’s metaphysics and his views on causation as part of the philosophical background for understanding the Five Ways. Attention is given to Aristotle’s explanations of change and his four causes: material, formal, efficient, and final. The chapter then examines Aquinas’s metaphysics of existence and his distinction between essence and existence, which features a contrast between caused and uncaused existence prominent in the Five Ways. There is a brief look at some more recent views of existence influenced by Immanuel Kant and others, which call Aquinas’s views into question. Finally, the chapter explains Aquinas’s model of explanation, that is, his views on what needs accounting for and how it is to be done. (There is some contrast with Gottfried Wilhelm Leibniz’s views.) Aquinas seeks a complete account for why contingently existing individual objects exist at all and undergo changes. He thinks that what has caused existence must ultimately be accounted for by what has uncaused existence.