Aquinas' "Third Way" - Argument for the Existence of God

Summary

In this philosophical discourse, Thomas Aquinas explores the rationale behind the existence of something rather than nothing. He introduces the concept of necessary and contingent truths and objects, using them to argue that not all things can be contingent. Aquinas posits that there must be at least one necessary being, which either derives its necessity from an external source or from within itself. He refutes the possibility of an infinite chain of causes, concluding that a necessary being must exist with its necessity originating from itself, which he equates to God.

Takeaways

• 📚 Thomas Aquinas discusses the question of why something exists rather than nothing in his influential works, 'Summa Theologiae' and 'Summa contra Gentiles'.
• 🔍 Aquinas introduces the concept of necessary truths, which are statements that are true and cannot be false, such as 'all bachelors are unmarried'.
• 🌐 He also explains contingent propositions, which are statements that are true but could possibly be false, like 'the desk is against the wall'.
• 🎯 Aquinas applies the idea of necessity and contingency to objects, stating that an object is contingent if it exists but could potentially not exist.
• 🌌 He argues that all contingent things, at some point, fail to exist, which implies that if everything were contingent, there would be a time when nothing existed.
• 🚫 Aquinas refutes the idea that all things are contingent by stating that if there was ever a time when nothing existed, then nothing would exist now, which contradicts the fact that things do exist.
• 🔑 He concludes that there must be at least one necessary thing that exists and cannot fail to exist, which is either caused by an external source or has its necessity from within itself.
• 🔄 Aquinas rejects the possibility of an infinite chain of causes, arguing that there must be a necessary being that starts the chain and has its necessity from within itself.
• 🌟 He identifies this necessary being as God, which is the ultimate explanation for the existence of everything else, concluding his Third Way argument for the existence of God.

Q & A

What is the main question Thomas Aquinas addresses in the script?

Thomas Aquinas addresses the question of why there is something rather than nothing, and why the universe exists at all.

In which two works of Thomas Aquinas does this argument appear?

The argument appears in Thomas Aquinas' 'Summa Theologiae' and 'Summa contra Gentiles'.

What is the difference between the two works where Aquinas presents this argument?

The 'Summa Theologiae' is written for believers who already believe in God, while 'Summa contra Gentiles' is a philosophical piece written without assuming any prior beliefs.

What is a necessary truth according to the script?

A necessary truth is a proposition that is true and cannot possibly be false, such as 'all bachelors are unmarried'.

What is a contingent proposition?

A contingent proposition is one that is true but could possibly be false, like 'the desk is against the wall' which could be moved.

What does it mean for an object to exist contingently?

An object exists contingently if it exists but could also fail to exist, such as a physical wall that could be destroyed.

Can you give an example of an object that exists necessarily according to the script?

The script suggests that the number seven might be an example of a necessary object, as it seems to exist and could not fail to exist.

What are the two assumptions Aquinas makes before presenting his argument?

The two assumptions are that some things are contingent and that all contingent things fail to exist at some time.

What is the conclusion Aquinas reaches if everything were contingent?

If everything were contingent, there would be a time when nothing existed, which would mean nothing would exist now, contradicting the fact that things do exist.

What does Aquinas argue about the necessity of a being?

Aquinas argues that at least one thing is necessary, meaning it exists and cannot fail to exist. This necessity could either come from an external source or from within itself.

Why does Aquinas reject the possibility of an infinite chain of causes?

Aquinas rejects the possibility of an infinite chain of causes because it would not have a starting point, which is necessary to explain the existence of everything else.

What is the final conclusion of Aquinas' Third Way argument?

The final conclusion is that there is a necessary being that exists and has its necessity from within itself, which Aquinas identifies as God.

Outlines

00:00

📚 Introduction to Aquinas' Argument

Thomas Aquinas explores the question of why there is something rather than nothing. He presents this argument in two of his works, 'Summa Theologia' aimed at believers and 'Summa contra Gentiles' as a philosophical piece for a broader audience. The paragraph introduces necessary truths, which are statements that cannot be false, and contingent propositions, which are true but could possibly be false. It also discusses the concept of objects existing contingently or necessarily, with examples to illustrate these philosophical concepts.

05:01

🌌 Contingent and Necessary Objects

This paragraph delves into the idea that some objects are contingent, meaning they exist but could potentially not exist. It contrasts this with necessary objects, which must exist and cannot not exist. The discussion includes the controversial notion of numbers like seven being necessary objects. The paragraph also introduces assumptions: that some things are contingent and that all contingent things will fail to exist at some point. It concludes with Aquinas' argument that if everything were contingent, there would have been a time when nothing existed, which contradicts the current existence of things.

10:03

🔗 The Impossibility of Infinite Chains

Aquinas argues against the possibility of an infinite chain of causes, suggesting that there must be a necessary being at the start of any chain of existence. This being would have its necessity from within itself, not from an external source. The paragraph explains that if such a being exists, it would be sufficient to explain the existence of all other things. Aquinas identifies this necessary being as God, concluding that this being, which has its necessity from within itself, is what we know as God. This argument is referred to as Aquinas' Third Way, one of five methods he uses to argue for the existence of God.

Keywords

💡Thomas Aquinas

Thomas Aquinas was a prominent theologian and philosopher of the Catholic Church. His works are foundational in Western philosophy and theology. In the video, Aquinas is discussed as the author of influential works such as 'Summa Theologica' and 'Summa Contra Gentiles,' where he presents arguments for the existence of God.

💡Necessary Truths

A necessary truth is a proposition that is true and cannot be false. In the context of the video, Aquinas uses the concept of necessary truths to argue that certain things exist necessarily, meaning they cannot not exist. An example given is 'all bachelors are unmarried,' which is a necessary truth because it is impossible for a bachelor to be married.

💡Contingent Propositions

Contingent propositions are those that are true but could possibly be false. The video script uses the example of 'the desk is against the wall,' which is contingently true because it could be moved and thus not against the wall. This concept is crucial in Aquinas's argument for the existence of God, as it leads to the conclusion that not all things can be contingent.

💡Contingent Objects

Contingent objects are those that exist but could potentially not exist. The video uses the example of a wall, which exists but could be destroyed and thus not exist. Aquinas argues that if all objects were contingent, there would have been a time when nothing existed, leading to the paradoxical conclusion that nothing would exist now.

💡Necessary Objects

Necessary objects are those that exist and cannot fail to exist. The video mentions the number seven as an example of a necessary object, suggesting that it exists independently of physical reality. This concept is central to Aquinas's argument for a necessary being that exists independently of contingent objects.

💡Summa Theologica

Summa Theologica is one of Aquinas's most influential works, written for believers to explain the rationality behind their belief in God. The video script discusses how this work contains Aquinas's argument for the existence of God, which is presented from the perspective of someone who already believes in God.

💡Summa Contra Gentiles

Summa Contra Gentiles is another significant work by Aquinas, written as a philosophical piece without assuming any prior beliefs in God. The video script notes that this work also contains Aquinas's argument for God's existence, but it is written in a way that is accessible to those who do not already believe in God.

💡Modus Tollens

Modus tollens is a form of deductive reasoning used in the video to argue that if all things were contingent, then there would be a time when nothing existed. Since it is false that nothing exists now, the argument concludes that not all things can be contingent. This logical structure is used to support Aquinas's argument for a necessary being.

💡Infinite Chain of Causes

The concept of an infinite chain of causes refers to a sequence of causes and effects that goes on indefinitely. Aquinas argues against the possibility of such a chain, suggesting that there must be a first cause or a necessary being that is not caused by anything else. This is a key point in his argument for the existence of God.

💡Parmenides

Parmenides was an ancient Greek philosopher whose ideas are referenced in the video to support the argument that something cannot come from nothing. This principle is used by Aquinas to argue that if there were a time when nothing existed, then nothing would exist now, which is a contradiction since we know things do exist.

💡Aristotle

Aristotle was a Greek philosopher whose ideas influenced Aquinas. The video mentions Aristotle's concept that an infinite chain of causes is not possible, which supports Aquinas's argument for a necessary being that is not caused by anything else. This is a crucial point in Aquinas's Third Way argument for the existence of God.

Highlights

Thomas Aquinas explores the question of why something exists rather than nothing.

Aquinas' argument appears in two different works: Summa Theologiae for believers and Summa contra Gentiles as a philosophical piece.

The concept of necessary truths is introduced, where a proposition is true and cannot be false.

Examples of necessary truths include 'all bachelors are unmarried' and 'triangles have three sides'.

Contingent propositions are those that are true but could possibly be false, such as 'the desk is against the wall'.

Objects can be contingent, existing but able to not exist, like a physical wall that could be destroyed.

An object exists necessarily if it exists and it's impossible for it to not exist, like the number seven.

Aquinas argues that not all things can be contingent because if they were, there would be a time when nothing existed.

If there was ever a time when nothing existed, then nothing would exist now, which is false.

At least one thing must be necessary, existing and not able to not exist.

Aquinas considers whether a necessary object gets its necessity from an external source or from within itself.

Aquinas argues against an infinite chain of causes, suggesting there must be a starting point of necessity.

The necessary being that starts the chain must have its necessity from within itself.

Aquinas concludes that this necessary being is God, which he identifies as his Third Way argument for the existence of God.

Aquinas' Third Way is one of five ways he argues for the existence of God.

Transcripts

Thomas Aquinas addresses this question

why is there something rather than

nothing it seems like it's possible that

nothing exists at all so why is it the

case that something at all exists why

does the universe exist now first of all

before we get into it most introductory

anthologies follow one of these

arguments but it actually appears in two

different places and Aquinas works he

has two influential works extremely

influential among dozens and dozens of

other works

one is the Summa theologia and it is

something that's written for believers

for people who already believe that God

exists and the other one is Summa contra

Ginty lays and it is written for as a

philosophical piece where you don't

presume any beliefs on the part of the

reader and both of them have this

argument and it seems odd to me that

most anthologies use the one from Simha

theologian

the one that kind of assumes the reader

is going to already have the belief that

God exists and this is just explaining

the rationality behind that belief

that's the one I'm following because

that's the most common one but we ought

to keep in mind there is a more expanded

version in some of his other works okay

some preliminaries in order to

understand this argument let's talk

about necessary truths a proposition is

necessarily true just in case that is if

and only if the proposition is true of

course that's required if it's

necessarily true it has to be true and

it's not possible for the proposition to

be false so what are some examples well

the statement that all bachelors are

unmarried is true it cannot possibly be

false you cannot find a Bachelor that's

married right

triangles have three sides one plus one

well I guess I have it written as one

plus two equals three I wasn't going to

say one plus one equals three I was

going to use one plus one equals two all

right just to clarify that one but we

can go on to talk about contingent

propositions a proposition is

contingently true just in case the

proposition is true and it is possible

for the proposition to be false so for

example the desk is against the wall it

is now but it could be pulled from the

wall Morgan Hall is north of stipes Hall

on the Western Illinois University

campus that's true

but they didn't have to build them that

way and it's possible that one of the

buildings not exists at all we'll talk

about that in a moment the refrigerator

is empty you get it from the store it's

empty but then of course it's possible

but that's false as you plug it in and

begin to use it and put food in it so

that's necessary and contingent truths

what we want to do is take roughly that

concept and apply it to objects so an

object is contingent it exists

contingently it is contingent or exists

contingently just in case if and only if

ok parallel first of all it has to exist

if we're going to talk about an object

that exists contingently has to exist

okay and it's possible that it not

exists so what kind of an example might

that be go ahead and think of something

that exists and could fail to exist now

if you're having trouble doing that turn

to your right

whatever you're looking at is probably

almost assuredly

fact it is it contingent odd so if I

turn to my right I see a wall it exists

but the wall could be broken down torn

down and fail to exist so almost

everything everything that we see with

our senses here taste touch these are

things that are like that even our

physical bodies things around us now an

object exists necessarily just in case

or if and only if of course it exists

and it's impossible for it to fail to

exist what would be an example of that

ah here not as easy to identify in fact

almost anything that we fill in as an

example is somewhat controversial so I

might you say the number seven which I

believe is a necessary object I'm not

talking about the numeral that you

scroll on a piece of paper I'm talking

about the number seven itself it seems

like that exists and could not fail to

exist it doesn't matter if every object

disappears that is physical it seems

like there would still be in number

seven as I preface this that's a

controversial statement some people

don't think of numbers that way Plato

would have all kinds of other things as

example platonic forms could go in into

this category okay so that's our

definitions of what we're going to be

talking about in the argument let's

consider now a couple assumptions first

of all some things are contingent now

that one is not a challenging assumption

at all we know this through a census

there might be a banana on the counter

it's contingent it exists but then you

can eat it and then it fails to exist so

that's pretty clear-cut and then second

all contingent things fail to exist at

some time and so Aquinas believes this

is built into the definition

we might even think of things that seem

like anything on earth I mean think of

the earth itself fails to exist at some

time according to current science I

believe it's about three and a half

billion years old maybe older than that

but in any case it can fail to exist at

some time likewise with the Sun failed

to exist in the past and if the

astronomers are correct billions of

years from now the Sun will also fail to

exist and of course when that happens

the earth will fail to exist as well so

even things that exist for billions of

years could fail to exist

alright we got that what's the argument

now that we have the concepts the

argument flows fairly quickly

it's very concise in the way that

Aquinas writes it and here's how I put

it if everything were contingent then

there would be a time at which nothing

existed now that's because all

contingent things can fail to exist and

eventually would fail to exist so if

everything were contingent there would

be a time at which all of them go out of

existence at once that's a possibility

but if

to happen if ever there were a time at

which nothing existed then nothing would

exist now going back to Parmenides you

can't have something from nothing so if

there was a time at which nothing

existed then nothing would exist now and

of course it's false that nothing exists

now most assuredly you exist at the

least but that means that not all things

are contingent when we put those three

premises together run a modus tollens a

couple times if you don't know what that

means it doesn't matter we have a valid

deductive argument at this point to

conclude that not all things are

contingent so now we know that if not

all things are contingent at least one

thing is necessary right that's just

assuming everything's either contingent

or necessary and that follows by

definition everything that exists either

can fail to exist or cannot fail to

exist so at least one thing is necessary

now if a thing is necessary Aquinas

considers this somewhat odd possibility

either it has the cause of its necessary

existence from an external source which

seems a little odd but maybe Aquinas

thought that we proposed that the number

seven was a necessary object and Aquinas

would seem to say this was I'll leave it

up to the Aquinas scholars whether he

actually does or not that the number

seven is a necessary object it exists

necessarily but it has its necessity

from God but we're not there yet all

right

another possibility is of course if you

have a necessary being that that being

has its necessity from within itself it

is necessary in itself so one of those

things have to be the case so something

exists that has the characteristics of

either A or B now if it's a Aquinas says

it's not possible that an infinite chain

this does not have to be in

time here now we just mean an infinite

chain of causes something that supports

another thing in existence it's positive

it's not possible that exists and this

comes from Aristotle of course so

there's a necessary being that starts to

chain again we're not talking about time

necessarily we're talking about being

the foundation for the existence of

something else maybe like fire and light

you know the when the fire exists it

causes the light to exist but they both

exist at the same time they both come

into existence at the same time somewhat

like that not a perfect analogy okay so

you can't have this infinite chain of

causes so you have to have a necessary

being that starts to chain and that

being has to have it's a necessity from

within itself and of course if B is true

you already have an object that has its

necessity from within itself so now we

know we have a necessary being that

exists and has its necessity from within

itself and Aquinas adds elsewhere it's

pretty clear if you have one you

shouldn't pause it anymore that suffice

is to explain everything else that

exists and if you haven't necessary

being there to exist and has its

necessity from within itself well of

course that necessary being is God we

know this being as God Aquinas says and

so that's his Third Way argument three

of five ways that he proves or argues

for the existence of God