Aquinas’ Proofs

1. Aquinas’ Proofs The five ways

2. Thomas Aquinas (1225-1274) • Joined Dominican order against the wishes of his family • Considered the most learned man of his day; much in demand as teacher and lecturer. • Strongly influenced by Aristotle • Summa Theologica never finished, following his ‘ecstasy’ in Dec. 1273

3. Aquinas on God’s existence • Believed, as against several interesting objections, that God’s existence can (and needs to be) ‘demonstrated’ (‘proved’, in the modern sense). • By this he meant 2 things: 1. Saying “God exists” is not a ‘self-evident’ statement. 2. That God exists is something which we can be completely sure of, as a matter of reason and logic and not simply of faith.

4. Is the existence of God self-evident? • “self-evident” = that which requires no proof in order to be known. **Perhaps what is and what isn’t “self evident may be something highly subjective. • 3 objections: the existence of God is self-evident because: I. Knowledge of God is innate II. The concept includes existence III. God is truth, & no one can consistently deny the existence of truth.

5. Answers to the objections • Objection 1: (Knowledge of God is innate) We know only in a vague way that God exists, and this is quite different from knowing absolutely that He exists. • Obj.2: (Concept includes existence) A distinction between mental and real existence maintained even in the case of “that than which no greater can be thought” (Ref. to Saint Anselm) • Obj.3: (God is truth…) This requires agreement on what “truth” actually is. • General rejoinder: what is self-evident cannot be denied, but “God is” can be denied. Therefore, “God is” is not self-evident (that is, his existence requires proof)

6. Objections to the idea that God’s existence can be proven • Objection 1: God’s existence is a matter of faith, not demonstration (reason) • Obj. 2: God, by definition, exceeds our understanding, therefore we can’t even know what it is we’re trying to prove the existence of • Obj.3: We can’t know God directly, only by his effects; but His effects (as finite objects or events) can’t tell us anything about His nature (which is, by definition, infinite). Therefore, we can’t prove anything about Him. (All that we “know” of in our life is finite.)

7. Replies to the objections • Objection 1: Anything which can be known by“natural reason” is not an article of faith -- something is an article of faith only if it cannot be known by other means. • Obj.2: We don’t need to know what God’s nature or essence is. We’re only proving the existence of We only are wanting to know that God exists. • Obj.3: As in 2, we’re only trying to prove that He exists and not anything about His nature. Every effect indicates, at the very least, the existence of its cause. General rejoinder: 2 ways of knowing or proving things: a priori (by someone telling you) and a posteriori(by some personal, rational experience or proof); God’s existence can only be proven in the latter way

8. Proof 1: argument from motion • “motion” - the argument here is better thought of as “the argument from change” • Change = going from potential to actual Acorn to a Tree (Aristotle) • Every ‘move’ or ‘change’ requires something else which brings about this change or motion • A chain of such ‘moves’ or ‘changes’ cannot be infinitely long • Therefore, there must be a ‘first mover’ (a first initiator of change), which is not itself moved; this first mover is God. (What Aristotle called “the unmoved mover”)

9. Aristotle’s 4 Causes • The material cause is the basic stuff out of which the thing is made. The material cause of a house, for example, would include the wood, metal, glass, and other building materials used in its construction. All of these things belong in an explanation of the house because it could not exist unless they were present in its composition. • The formal cause {Gk. eidos [eidos]} is the pattern or essence in conformity with which these materials are assembled. Thus, the formal cause of our exemplary house would be the sort of thing that is represented on a blueprint of its design. This, too, is part of the explanation of the house, since its materials would be only a pile of rubble (or a different house) if they were not put together in this way. • The efficient cause is the agent or force immediately responsible for bringing this matter and that form together in the production of the thing. Thus, the efficient cause of the house would include the carpenters, masons, plumbers, and other workers who used these materials to build the house in accordance with the blueprint for its construction. Clearly the house would not be what it is without their contribution. • Lastly, the final cause {Gk. telo [télos]} is the end or purpose for which a thing exists, so the final cause of our house would be to provide shelter for human beings. This is part of the explanation of the house's existence because it would never have been built unless someone needed it as a place to live.

10. Proof 2: argument from efficient cause • Aquinas, following Aristotle, recognizes four kinds of ‘causes’ (4 kinds of ‘why’): formal, material, final, and efficient causes • Nothing is the efficient cause of itself; therefore, for every effect there must exist some efficient cause distinct from the effect • Such a chain of causes cannot go on to infinity; therefore there is a first cause (and that is God)

11. Proof 3: argument from possibility • Everything which exists, exists only contingently (that is, it is possible that it could not exist) • Any contingent being must have, at some time, not existed (if it is possible that it does exist at this time, then necessarily it did not exist at some time) – remember, all things we know of have a beginning and an end – are finite • The world, taken as a whole & as contingent, must have at some time therefore not existed • But what once did not exist must come to exist by virtue of something which itself does exist. • That necessary being (or efficient cause) is God.

12. Proof 4: argument from gradation • Every quality or attribute which can be thought of in terms of degree, is referenced to some standard (more or less good to some standard of goodness, more or less red to some standard of redness, etc.) • Since being admits of degrees (as does goodness & every other sort of perfection), there must be something which is the standard for that attribute (a formal cause of that attribute) • That standard is God • (This proof is more Platonic than Aristotelian.)

13. Proof 5: argument from design • Natural kinds and events are only understood properly as having an end state or aim • Such non-intelligent things can act towards such ends only by being directed by something which is intelligent (something which could have motives or purposes) • Therefore there is an intelligent being which directs natural kinds and events; and that being is God.