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Theology 9
Directions: Each group will be assigned one of St. Thomas Aquinas’ proofs. In your group, read through the information provided for
that proof and then in your own words describe what the proof is saying. Make sure to be thorough. Your group is the expert of this
proof and will teach the class about the proof.
St. Thomas Aquinas: The Existence of God can be proved in five ways.
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What real evidence can be supplied for God's existence? St. Thomas, in his Summa Theologica, sets forth five separate
proofs for the existence of God. St. Thomas' proofs rely on the world of our experience-what we can see around us. In these
proofs we can easily see the influence of Aristotle and his doctrine of the Four Causes.
The First Way: Argument from Motion
The Proof from Motion. We observe motion all around us. Whatever is in motion now was at rest until moved by
something else, and that by something else, and so on. But if there were an infinite series of movers, all waiting to
be moved by something else, then actual motion could never have got started, and there would be no motion now.
But there is motion now. So there must be a First Mover, which is itself unmoved. This First Mover we call God.
1. Our senses prove that some things are in motion.
2. Things move when potential motion becomes actual motion.
3. Only an actual motion can convert a potential motion into an actual motion.
4. Nothing can be at once in both actuality and potentiality in the same respect (i.e., if both actual and
potential, it is actual in one respect and potential in another).
5. Therefore nothing can move itself.
6. Therefore each thing in motion is moved by something else.
7. The sequence of motion cannot extend ad infinitum.
8. Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone
understands to be God.
In your own words:
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The Second Way: Argument from Efficient Causes
The Proof from Efficient Cause. Everything in the world has its efficient cause--its maker--and that maker has its
maker, and so on. The coffee table was made by the carpenter, the carpenter by his or her parents, and on and
on. But if there were just an infinite series of such makers, the series could never have got started, and therefore
be nothing now. But there is something everything there is! So there must have been a First Maker, that was not
itself made, and that First Maker we call God.
1. We perceive a series of efficient causes of things in the world.
2. Nothing exists prior to itself.
3. Therefore nothing is the efficient cause of itself.
4. If a previous efficient cause does not exist, neither does the thing that results.
5. Therefore if the first thing in a series does not exist, nothing in the series exists.
6. The series of efficient causes cannot extend ad infinitum into the past, for then there would be no things
existing now.
7. Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God.
In your own words:
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The Third Way: Argument from Possibility and Necessity (Reductio argument)
The Proof from Necessary vs. Possible Being. Possible, or contingent, beings are those, such as cars and trees and you
and I, whose existence is not necessary. For all such beings there is a time before they come to be when they are not yet,
and a time after they cease to be when they are no more. If everything were merely possible, there would have been a time,
long ago, when nothing had yet come to be. Nothing comes from nothing, so in that case there would be nothing now! But
there is something now-the world and everything in it-so there must be at least one necessary being. This Necessary Being
we call God.
1. We find in nature things that are possible to be and not to be, that come into being and go out of being i.e., contingent
beings.
2. Assume that every being is a contingent being.
3. For each contingent being, there is a time it does not exist.
4. Therefore it is impossible for these always to exist.
5. Therefore there could have been a time when no things existed.
6. Therefore at that time there would have been nothing to bring the currently existing contingent beings into existence.
7. Therefore, nothing would be in existence now.
8. We have reached an absurd result from assuming that every being is a contingent being.
9. Therefore not every being is a contingent being.
10. Therefore some being exists of its own necessity, and does not receive its existence from another being, but rather
causes them. This all men speak of as God.
In your own words:
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The Fourth Way: Argument from Gradation of Being
The Proof from Degrees of Perfection. We all evaluate things and people in terms of their being more or less
perfectly true, good, noble and so on. We have certain standards of how things and people should be. But we
would have no such standards unless there were some being that is perfect in every way, something that is the
truest, noblest, and best. That Most Perfect Being we call God.
1. There is a gradation to be found in things: some are better or worse than others.
2. Predications of degree require reference to the “uttermost” case (e.g., a thing is said to be hotter according
as it more nearly resembles that which is hottest).
3. The maximum in any genus is the cause of all in that genus.
4. 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.
In your own words:
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The Fifth Way: Argument from Design
The Proof from Design. As we look at the world around us, and ourselves, we see ample evidence of design--the
bird's wing, designed for the purpose of flight; the human ear, designed for the purpose of hearing; the natural
environment, designed to support life; and on and on. If there is design, there must be a designer. That Designer
we call God
1. We see that natural bodies work toward some goal, and do not do so by chance.
2. Most natural things lack knowledge.
3. But as an arrow reaches its target because it is directed by an archer, what lacks intelligence achieves goals
by being directed by something intelligence.
4. Therefore some intelligent being exists by whom all natural things are directed to their end; and this being
we call God
In your own words:
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