Ethos Education

Aquinas’ Cosmological Arguments

Alevel Aquinas

coverThis A Level RE lesson uses a free downloadable clip from Arguments For The Existence of God published by Oxford University Press.

It is designed to support teaching of the following modules in the new exam specifications:

  • AQA: Component 1 (Section B)
  • EDEXCEL: Paper 1 (1.2)
  • OCR: Philosophy of Religion Paper 1 (Section B)
  • WJEC: Component 2 (AS) (Theme 1)

For this lesson you will need to download:

DOWNLOAD Aquinas’ Cosmological Arguments:  mp4 (high-res)mp4 (low-res) / wmv / (help) (2 min 48 s)

Graphic of Aquinas third way worksheet1 graphic of aquinas third way worksheet2

Before you teach the lesson:

please complete surveyRead this professional development background material, or book an online masterclass on this area of philosophy.

The argument

  • Aquinas’ argument can be summarised as follows:
    • If everything is contingent (is generated, and perishable), given infinite time (thus, infinite possibilities) at some point there could have been nothing.
    • Things can’t come out of nothing.
    • Things are in existence.
    • Therefore, there must always have been something. That something must have necessary existence, and be the ultimate reason for all other things.
  • The key to this argument is Aquinas’ definition of ‘contingent’.
    • To modern philosophers ‘contingent’ means ‘logically possible not to be’. And if this were the case, Aquinas’ argument would not be sound.
    • However, Aquinas means by ‘contingent’ something that can (and does) regularly go from non-existent to existent and vice-versa. As Edward Feser puts it: ‘They have no potency or potential for changeless, indefinite existence; hence they cannot exist indefinitely.’ (Aquinas, Edward Feser, Oneworld Publications, 2009, p. 92)
  • Brian Davies offers a very different interpretation of Aquinas’ argument, stating that Aquinas does not believe in infinite time nor in the provable temporal beginning of the world. Davies’ interpretation relies primarily upon causal reasoning and goes thus (Aquinas’ Third Way, Brian Davies, New Blackfriars, Vol. 82, No. 968 October 2001, p. 462):
    • Contingent things come about by something else.
    • If there were only contingent things, there would be nothing.
    • There isn’t nothing.
    • Therefore, there must be a necessary thing which exists.

Useful stories

  • G.K. Chesterton tells the story of a woman who picked up Aquinas’ Summa Theologica and read The Simplicity of God. She then laid down the book with a sigh and said, ‘Well, if that’s His simplicity, I wonder what His complexity is like.’
  • Aquinas was a Dominican who spent his public life arguing strongly for the freedom of the Friars to roam as they please, and for the harmony of religion and science. He held that science rightly claims the realm of the natural, and theology the realm of the supernatural.

Background reading

enquire masterclass

Lesson Plan

please complete surveyUse (or adapt as appropriate) this plan for your lesson.

Learning Objectives

  • Understand the argument in Aquinas’ Third Way.
  • Understand and evaluate criticisms of Aquinas’ Third Way.


  • Watch the video Aquinas’ Cosmological Arguments (preview and download above).
  • Clarify the argument with the students. Ask them to express it back to you.
  • Explain that this video has introduced them to Aquinas and his Cosmological Arguments. In this lesson we will look at his third argument – usually referred to as Aquinas’ Third Way.

Main Activities

  • Hand out Worksheet 1 and read through the passage as a class, clarifying points as you go.
    • Ask the students to work through the questions.
    • Feedback the students’ answers.
  • Lead this on to a student Q&A. Let them ask questions, and also pose some yourself:
    • Can you prove the existence of God just by thinking about it?
    • What’s the biggest weakness of this argument?
    • Is there any way of strengthening Aquinas’ argument?
    • Is it true that something can’t be produced out of nothing?
  • If appropriate, show again the video Aquinas’ Cosmological Arguments (preview and download above).
  • Hand out Worksheet 2 and read through the passage as a class, clarifying points as you go.
    • Ask the students to work through the questions.

Evaluation of Learning

  • Ask students to present their responses in small groups.
  • Encourage debate between students who disagree.
  • If all students agree, split into two sides and allocate beliefs.
  • Moderate the debate and give students positive feedback about their knowledge and arguments.

See also:

Alevel Kant obj

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