Chapter 5 examines the Second Way, which starts from observing an ordering of efficient causes in the world and concludes to a first uncaused cause, which is God. After giving the translation and premises of the Second Way, I briefly compare the First and Second Ways and then look at what efficient causation involves for Aquinas. The rest of this short chapter considers the Big Bang as a rival account of the origin of the universe to invoking a divine nature. The chapter closes by briefly considering a multiverse.

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.