Five Ways Quinque Viae

The Five Ways (Quinque Viae) of Saint Thomas Aquinas are 5 philosophical proofs of the existence of Almighty God and of His Divine Attributes.

The Five Ways

Saint Thomas summarizes all Christian knowledge of God through reason into five broad categories: "On the contrary, It is said in the person of God: "I am Who am." (Exodus 3:14)

I answer that, The existence of God can be proved in five ways.

The First Way

The first and more manifest way is the argument from motion. It is certain, and evident to our senses, that in the world some things are in motion. Now whatever is in motion is put in motion by another, for nothing can be in motion except it is in potentiality to that towards which it is in motion; whereas a thing moves inasmuch as it is in act. For motion is nothing else than the reduction of something from potentiality to actuality. But nothing can be reduced from potentiality to actuality, except by something in a state of actuality. Thus that which is actually hot, as fire, makes wood, which is potentially hot, to be actually hot, and thereby moves and changes it. Now it is not possible that the same thing should be at once in actuality and potentiality in the same respect, but only in different respects. For what is actually hot cannot simultaneously be potentially hot; but it is simultaneously potentially cold. It is therefore impossible that in the same respect and in the same way a thing should be both mover and moved, i.e. 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. But this cannot go on to infinity, because then there would be no first mover, and, consequently, no other mover; seeing that subsequent movers move only inasmuch as they are put in motion by the first mover; as the staff moves only because it is put in 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

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

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

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

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.

Syllogistic Summaries of the Five Ways

For modern readers, who may not be familiar with all the technical terms used by St. Thomas, a syllogistic summary in modern philosophical language.

I: The First Way (also known as the Demonstration from motion, or alternately the Demonstration from Potentiality)

1. All that is moved (or that has had some potency actualized) has been put in motion (or has been actualized) by another.

2. If every thing set in motion (or actualized) were moved (i.e. in a state of potency needing to be actualized), there would be an infinite regress.

3. Therefore, there is a Mover that is Unmoved. (or, a Being that is Pure Actuality, in Whom there is no potentiality).

This Being terminates the chain of motion and is Who is called God. It is He Who, lacking potentiality (there is nothing that He can become that He is already not), set all other things in motion - He actualizes the potential other beings have by moving them from one state to another.

For an analogy, if one could observe balls being set in motion, by one ball striking the next and moving it, you could deduce that the line of balls (even if one could not see the first mover) does not go on indefinitely, but will have to terminate in some mover - of a nature other than a moved ball (e.g. a human hand).

The difference between the First Way and the Second Way is the first deals with motion/potentiality while the second deals with cause/being itself. Some non-theists may admit only one or the other, hence the Angelic Doctor takes the trouble to prove the same Truth in different ways, so that many people can be led to acknowledge it.

II: The Second Way (also known as the Demonstration from efficient causes leading up to a first Cause)

1. In the world it is seen that nothing can be the cause of itself, otherwise it would exist prior to itself

2. Therefore, every thing that begins to exist has a cause of its existence.

3. It cannot be that every being is caused by another being, otherwise there will be no end.

4. Therefore, a first being exists, without beginning, and as first cause of all beings.

III: The Third Way - Demonstration from Contingency/Necessity (also known as the Demonstration from the possible and the necessary)

1. Beings are said to exist contingently when their non-existence is possible (i.e. for instance, they can cease to exist, they at one time did not exist etc)

2. Every contingent being depends on another being for its existence. No contingent being, that began to exist, can be its own cause.

3. Therefore, if every being in existence existed contingently, the series would never end, and no existence would be possible.

4. Therefore, it is necessary that some Being exists not contingently, but necessarily, i.e. without beginning and end.

IV: The Fourth Way: Demonstrations of God's Attributes - the Supreme Being possesses every perfection in its highest possible plenitude

In the Fourth Way, St. Thomas proves God is infinite Goodness and infinite Perfection. This follows from the gradation we observe in created things. We see that some are more or less good, more or less beautiful and so on. But what is Goodness that is differently participated in by different beings? What is the origin of the moral law we discern on our conscience, that reason and the natural law inform us is eternal and immutable? Each of these predications suggest an infinite source of all these attributes which they display in a limited way. Just as we saw that being and motion must be caused, so now we see that goodness and beauty and each particular attribute has its source in God.

1. Different modes of being that require causes are observed, as well as even different grades of being e.g. beings more or less good, and other such participations in which creatures share in different degrees.

2. As it is clear modes of being require a cause, the gradations of being also require a specific cause, e.g. gradations of temperature caused by heat.

3. Therefore, there exists some Being that is uttermost Goodness, uttermost Beauty, uttermost Wisdom and uttermost Love.

4. As for the areas where these are absent, which non-Christians sometimes wonder about, it is because all creatures have not yet fulfilled there end, which is union with this Goodness, which is therefore the purpose to work toward. Evil arises in creation from free choices that are morally sinful.

V: The Fifth Way: Demonstrations drawn from Intelligent Design and the Physical Laws of the Universe. Creatures acting for an end:

In the Fifth, God's Intelligence and Wisdom is deduced from the laws of the created universe and the design inherent in nature. The universe like a programmed algorithm behaves in ordered ways, manifesting an Intelligence working behind the scenes that governs all things. St. Thomas here argues that physical laws themselves are already sufficient evidence of Intelligent Design, which ought to lead righteous minds to their Eternal Creator.

1. Unintelligent things constantly move toward an end, e.g. orbiting planets, as if guided by an Intelligent Being

2. Things which lack intelligence are not capable of doing so, unless guided to do so by a Being that has Intelligence.

3. Therefore, the laws of Nature, like arrows directed by an archer, work toward a fixed end because of the Intelligence that guides them.

4. In other words, God constantly guides created things by His laws. The universe behaves liked an algorithm or programmed system.

These five proofs or five ways to arrive at the knowledge of God through reason are a supreme demonstration of the Truth of what St. Paul the Apostle says in his epistle to the Romans: "For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse:" (Rom 1:20).