Encyclopedia of Philosophy: Thomas Aquinas

« them being there).11 But God is also the final cause of creatures, that to which they aim, tend, or return (reditus),that which contains the perfection or goal of all created things.12 According to Aquinas, everything comes from Godand is geared to him.

God accounts for there being anything apart from himself, and he is what is aimed at byanything moving towards its perfection.

Aristotle says that everything aims for its good (Ethics I, i, 1094a3).Aquinas says that any created good derives from God who contains in himself all the perfections found in creatures.In so far as a creature moves to its perfection, Aquinas goes on to argue, the creature is tending to what is to befound in God himself.13 As Father, Son, and Spirit, Aquinas adds, God is the special goal of rational individuals.

Forthese can share in what God is by nature.14Aquinas is sometimes reported as teaching that someone who claims rationally to believe in the existence of Godmust be able to prove that God exists.

But this is not what Aquinas teaches.

He says that people can have a rational belief in the existence of God without being able to prove God's existence.15 And he holds that,apart from the question of God's existence, people may be rational in believing what they cannot prove.

FollowingAristotle, he maintains that people may rationally believe indemonstrable principles of logic.16 He also maintains thatone may rationally believe what a teacher imparts to one, even though one is in no position to demonstrate thetruth of what the teacher has told one.17 He does, however, contend that belief in God's existence is one for whichgood philosophical reasons can be given.

This is clear from Summa theologiae Ia, 2, 2 and Summa contra Gentiles I,9, where he says that ‘we can demonstrate...that God exists' and that God can be made known as we ‘proceedthrough demonstrative arguments'.

‘Demonstrative arguments' here means what it does for Aristotle, i.e.

argumentsusing premisses which entail a given conclusion on pain of contradiction.Aquinas denies that proof of God's existence is given by arguing that ‘God does not exist' is a contradiction.

So herejects the suggestion, commonly associated with St Anselm, that the existence of God can be demonstrated fromthe absurdity of denying that God exists.18 He also rejects the view that human beings are naturally capable ofperceiving or experiencing God as they perceive or experience the things with which they are normally acquainted.According to Aquinas, our perception and seeing of things is based on sensory experience.19 Since God is not aphysical object, Aquinas concludes that there can be no natural perception or seeing of God on the part of humanbeings.20 He does not deny that people might have a knowledge of God without the medium of physical objects.

Intalking of life after death, he says that people can have a vision of God which is nothing like knowing a physicalobject.21 But he denies that human beings in this world have a direct and unmediated knowledge of God.

On hisaccount, our knowledge of God starts from what we know of the world in which we live.

According to him, we canknow that God exists because the world in which we find ourselves cannot account for itself.Aquinas considers whether we can prove that God exists in many places in his writings.

But his best-knownarguments for the existence of God come in Ia, 2, 3 (the ‘Five Ways').

His thinking in this text is clearly indebted toearlier authors, especially Aristotle, Maimonides, Avicenna and Averroes.22 And it would be foolish to suggest thatthe reasoning of the Five Ways can be quickly summarized in a way that does them justice.

But their substance canbe indicated in fairly uncomplicated terms.In general, Aquinas's Five Ways employ a simple pattern of argument.

Each begins by drawing attention to somegeneral feature of things known to us on the basis of experience.

It is then suggested that noneof these features can be accounted for in ordinary mundane terms, and that we must move to a level of explanationwhich transcends any with which we are familiar.23Another way of putting it is to say that, according to the Five Ways, questions we can raise with respect to whatwe encounter in day to day life raise further questions the answer to which can only be thought of as lying beyondwhat we encounter.Take, for example, the First Way, in which the influence of Aristotle is particularly prevalent.24 Here the argumentstarts from change or motion in the world.25 It is clear, says Aquinas, that there is such a thing—he cites as aninstance the change involved in wood becoming hot when subjected to fire.26 How, then, may we account for it?According to Aquinas, anything changed or moved is changed or moved by something else.

Omne quod movetur abalio movetur.

This, he reasons, is because a thing which has changed has become what it was not to begin with,which can only happen if there is something from which the reality attained by the thing as changed somehowderives.27 Therefore, he concludes, there must be a first cause of things being changed or moved.

For therecannot be an endless series of things changed or moved by other things.

If every change in a series of connectedchanges depends on a prior changer, the whole system of changing things is only derivatively an initiator of changeand still requires something to initiate its change.

There must be something which causes change or motion in thingswithout itself being changed or moved by anything.

There must an unchanged changer or an unmoved mover.Anything which is moved is moved by something else...

To cause motion is to bring into being what was previouslyonly able to be, and this can only be done by something that already is...

Now the same thing cannot at the sametime be both actually x and potentially x, though it can be actually x and potentially y: the actually hot cannot atthe same time be potentially hot, though it can be potentially cold.Consequently, a thing which is moved cannot itself cause that same movement; it cannot move itself.

Of necessitytherefore anything moved is moved by something else...

Now we must stop somewhere, otherwise there will be nofirst cause of the movement and as a result no subsequent causes...

Hence one is bound to arrive at some firstcause of things being moved which is not itself moved by anything, and this is what everybody understands by God.(Summa theologiae I q.

2, a.

3)If we bear in mind that Aquinas believes that time can be said to exist because changes occur, the First Way isarguing that the reality of time is a reason for believing in God.28 Aquinas is suggesting that the present becomesthe past because something non-temporal enables the present to become past.The pattern of the First Way is repeated in the rest of the Five Ways.

According to the Second Way, there arecauses in the world which bring it about that other things come to be.

There are, as Aquinas puts it, causes whichare related as members of a series.

In that case, however, there must be a first cause, or something which is not. »