The design (teleological) argument

Design arguments infer a designer from apparent order, regularity and purpose in nature.

• Aquinas' Fifth Way (Summa Theologica, I, Q2, a3): natural bodies without intelligence act towards an end, as an arrow is directed by an archer — so they are directed by an intelligent being "whom we call God."
• William Paley (Natural Theology, 1802): finding a watch on a heath, its parts fitted to a purpose imply a watchmaker; the eye and the universe show the same contrivance, so imply a Designer.
• F. R. Tennant (Philosophical Theology, 1928–30): the anthropic argument (the cosmos is fine-tuned for life) and the aesthetic argument (we appreciate beauty beyond survival needs).

Paley's analogy

Challenges to design

• David Hume (Dialogues Concerning Natural Religion, 1779): the analogy is weak (the universe is unique and more like a growing organism than a machine); the order could have many designers, an imperfect or apprentice god, or arise by chance (the Epicurean hypothesis).
• Charles Darwin (On the Origin of Species, 1859): natural selection offers a non-purposive mechanism for apparent design.
• J. S. Mill (Nature, 1874): nature's cruelty and waste count against a wholly good, wise designer.

Hume on analogy

The cosmological argument

Cosmological arguments reason from the existence of the universe to a cause or explanation of it.

• Aquinas' first three Ways: from motion (an unmoved mover), efficient causation (a first cause) and contingency (things that need not exist must depend on a necessary being).
• Leibniz: the Principle of Sufficient Reason — everything has an explanation; the whole contingent series still needs a sufficient reason outside itself, namely a necessary being.

Contingency

Challenges to the cosmological argument

• Hume: the "fallacy of composition" — what is true of each part (having a cause) need not be true of the whole; and we have no experience of universe-making to reason from.
• Bertrand Russell (BBC radio debate with F. C. Copleston, 1948): the universe may be a brute fact — "the universe is just there, and that's all."
• Kant: causation applies within experience; we cannot legitimately extend it beyond the world to a first cause.

The ontological argument

A wholly a priori argument: God's existence follows from the concept of God alone.

• Anselm (Proslogion, 1078): God is "that than which nothing greater can be conceived." A being that exists in reality is greater than one existing only in the mind — so God must exist in reality (ch. 2); and must exist necessarily (ch. 3).
• Descartes (Meditation V): existence belongs to God's essence as three angles belong to a triangle, or a valley to a mountain — a supremely perfect being cannot lack existence.

Anselm's definition

Challenges to the ontological argument

• Gaunilo ("On Behalf of the Fool"): the same logic would prove a perfect island must exist — a reductio ad absurdum.
• Kant: existence is not a real predicate — saying a thing exists adds nothing to its concept, so you cannot define God into existence.

Kant's objection

A priori, a posteriori, or objection?

Sort each item into whether it reasons from concepts alone (a priori), from experience of the world (a posteriori), or is a challenge.

Scholar to claim

Match each thinker to the claim they are best known for.

The big ideas to know

For AS/A-level essays, always weigh whether the argument succeeds, not just what it says. Press Finish to see your score.