The following is the minimum you would want to know about the Cosmological Argument for the exam:

• A Cosmological Argument is an argument which reasons from observations about the universe (or ‘Cosmos’) to the origins of the universe as a whole.

• Cosmological Arguments are a posteriori because they depend on observations of the world.

• For this reason, they are inductive — leading to probability rather than certainty.

• Here we examine the most famous Cosmological Argument: Thomas Aquinas’s ‘Five Ways’.

The First Way

• Things in the world are always changing.

  • N.B. Many translations of Aquinas use ‘motion’, but he means ‘change’. His specific example is a piece of wood catching fire.

• However, nothing in the world can change on its own.

• As Aquinas says, ‘everything that is moved [changed] must be moved [changed] by another’ (ST I, Q. 2, Art. 3).

• But this chain of changes cannot have existed forever: at some point something MUST have been the cause of its own motion/change.

• This ‘something’ is God.

The Second Way

• Everything that exists has an efficient cause.

  • N.B. This term is borrowed from Aristotle; it basically means ‘a creator’, e.g. the efficient cause of a statue is its sculptor.

• However, as we read in Aquinas, ‘we do not find — nor is it possible to find — anything that is an efficient cause of its own self’ (ST I, Q. 2, Art. 3).

• So, everything must have an efficient cause. But this chain of efficient causes cannot go on forever: at the start of it there must have been a ‘first efficient cause’ — something that was its own efficient cause.

• This ‘something’ is God.

The Third Way

• Everything that exists is contingent; that is, it depends on other things for its existence, and cannot exist if they do not exist.

• However, as Aquinas explains ‘it is impossible to go on to infinity among necessary beings that have a cause of their necessity’ (ST I, Q. 2, Art. 3).

• There must be at least one necessary being, which does not depend on anything for its existence, but has simply always existed.

• This ‘necessary being’ is God.

References:

• Aquinas, Thomas. n.d. 'New English Translation of St. Thomas Aquinas's Summa Theologiae (Summa Theologica)', trans. Alfred J. Freddoso <https://www.freddoso.com/summa-translation/TOC.htm> [accessed 02 June 2026]