Five Ways (Aquinas)



The Quinque viæ (Latin for "Five Ways") (sometimes called "five proofs") are five logical arguments for the existence of God summarized by the 13th-century Catholic philosopher and theologian Thomas Aquinas in his book Summa Theologica. They are:


 * 1) the argument from "first mover";
 * 2) the argument from universal causation;
 * 3) the argument from contingency;
 * 4) the argument from degree;
 * 5) the argument from final cause or ends ("teleological argument").

Aquinas expands the first of these – God as the "unmoved mover" – in his Summa contra Gentiles.

Quotes

 * The existence of God may be proved in five ways. The first and most manifest way is the argument from motion. ...Whatever is in motion is moved by another, for nothing can be in motion except it have a potentiality for that toward which it is being moved. ...It is ...impossible that from the same point of view and in the same way anything should be both moved and mover, or that it should move itself. Therefore, whatever is in motion must be put in motion by another. If that by which it is put in motion be itself put in motion, then this also must needs be put in motion by another, and that by another again. This cannot go on to infinity, because then there would be no first mover; as the staff only moves because it is put into motion by the hand. Therefore it is necessary to arrive at a First Mover, put in motion by no other; and this everyone understands to be God.
 * The second way is from the nature of the efficient cause. In the world of sense we find there is an order of efficient causes. There is no case known (neither is it, indeed, possible) in which a thing is found to be the efficient cause of itself; for so it would be prior to itself, which is impossible. Now in efficient causes it is not possible to go on to infinity, because in all efficient causes following in order, the first is the cause of the intermediate cause, and the intermediate is the cause of the ultimate cause, whether the intermediate cause be several, or only one. Now to take away the cause is to take away the effect. Therefore, if there be no first cause among efficient causes, there will be no ultimate, nor any intermediate cause. But if in efficient causes it is possible to go on to infinity, there will be no first efficient cause, neither will there be an ultimate effect, nor any intermediate efficient causes; all of which is plainly false. Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God.
 * The third way is taken from possibility and necessity, and runs thus. We find in nature things that are possible to be and not to be, since they are found to be generated, and to corrupt, and consequently, they are possible to be and not to be. But it is impossible for these always to exist, for that which is possible not to be at some time is not. Therefore, if everything is possible not to be, then at one time there could have been nothing in existence. Now if this were true, even now there would be nothing in existence, because that which does not exist only begins to exist by something already existing. Therefore, if at one time nothing was in existence, it would have been impossible for anything to have begun to exist; and thus even now nothing would be in existence � which is absurd. Therefore, not all beings are merely possible, but there must exist something the existence of which is necessary. But every necessary thing either has its necessity caused by another, or not. Now it is impossible to go on to infinity in necessary things which have their necessity caused by another, as has been already proved in regard to efficient causes. Therefore we cannot but postulate the existence of some being having of itself its own necessity, and not receiving it from another, but rather causing in others their necessity. This all men speak of as God.
 * The fourth way is taken from the gradation to be found in things. Among beings there are some more and some less good, true, noble and the like. But "more" and "less" are predicated of different things, according as they resemble in their different ways something which is the maximum, as a thing is said to be hotter according as it more nearly resembles that which is hottest; so that there is something which is truest, something best, something noblest and, consequently, something which is uttermost being; for those things that are greatest in truth are greatest in being, as it is written in Metaph. ii. Now the maximum in any genus is the cause of all in that genus; as fire, which is the maximum heat, is the cause of all hot things. Therefore there must also be something which is to all beings the cause of their being, goodness, and every other perfection; and this we call God.
 * The fifth way is taken from the governance of the world. We see that things which lack intelligence, such as natural bodies, act for an end, and this is evident from their acting always, or nearly always, in the same way, so as to obtain the best result. Hence it is plain that not fortuitously, but designedly, do they achieve their end. Now whatever lacks intelligence cannot move towards an end, unless it be directed by some being endowed with knowledge and intelligence; as the arrow is shot to its mark by the archer. Therefore some intelligent being exists by whom all natural things are directed to their end; and this being we call God.


 * Thomas Aquinas, Summa Theologica (1265–1274) I, Q.2, Art. 3, Obj. 2 in The "Summa Theologica" of St. Thomas Aquinas (1911) Tr. Fathers of the English Dominican Province, Vol. 1, pp. 24-25.

Quotes on the Five Ways of Aquinas

 * A cosmological argument is an argument to the existence of God from the existence of some finite object or, more specifically, a complex physical universe. There have been many versions of the cosmological argument given over the past two-and-a-half millennia; the most quoted are the second and third of Aquinas’s five ways to show the existence of God. However, Aquinas’s ‘five ways’, or rather the first four of his five ways, seem to me to be one of his least successful pieces of philosophy.
 * Richard Swinburne, The Existence of God, Clarendon Press, Oxford, 2nd Edition, pp. 136-137. ISBN 0–19–927168–2


 * [T]he Five Ways fail […] principally because it is much more difficult than at first appears to separate them from their background in medieval cosmology. Any contemporary cosmological argument would have to be much more different from the arguments of Aquinas than scholastic modernizations customarily are.
 * Anthony Kenny, The Five Ways: St. Thomas Aquinas' Proofs of God's Existence, New York: Routledge (2003), pp. 3-4


 * Aquinas believes that human beings (even in our earthly condition here below) can have knowledge, scientific knowledge of God's existence, as well as knowledge that he has such attributes as simplicity, eternità, immateriality, immutability, and the line. In Summa Theologiae Aquinas sets out his famous Five Ways or five proofs of God's existence: in Summa Contra Gentiles he sets out the proof from motion in much greater detail; and in each case he follows these alleged demonstrations with alleged demonstrations that God possesses the attributes just mentioned. So natural knowledge of God is possible. [...] So most of those who believe in God do so on faith. Fundamentally, for Aquinas, to accept a proposition on faith is to accept it on God's authority; faith is a manner of "believing God" (ST, IIa, IIae, ii, 2) "for that which is above reason we believe only because God has revealed it" (SCG, I, 9).
 * Alving Plantinga, The Analytic Theist: An Alving Plantinga Reader, Wm. B. Eerdmans Publishing, 1998. ISBN 9780802842299. Ch. "Reason and Belief in God: Reformed Epistemology'', pp. 125-126