PHLA10S 4

Philosophy of Religion

PHLA10S 4

Philosophy of Religion

Logic Puzzle 1

In the land of the knights and knaves. Knights always tell the truth. Knaves always lie. If two people are both knights, or both knaves we say that are of the ‘same type’.

1. You meet A, B and C.

A says “B is a knave”.B says “A and C are of the same type”.

What is C?

2. You meet A, B and C.

A says “B and C are of the same type”.Someone asks C: “Are A and B the same type?”

What does C answer?

PHLA10S 4

Philosophy of Religion

Logic Puzzle 2In the land of the knights and knaves AND normals. Knights always tell the truth. Knaves always lie. Normals sometimes tell the truth and sometimes lie.

Also, it is a law that knights can only marry knaves, and knaves can onlymarry knights. (So who can normals marry?)

1. You meet A, B and C. Exactly one of of them is a knight, one normal and one a knave.

A says “I am normal”.B says “That is true”.

C says “I am not normal”.What are A, B and C?

2. You meet two individuals A and B who are a married couple.

A says “my spouse is not normal”.B says “my spouse is not normal”

What A and B?

PHLA10S 4

Faith and Reason

● Philosophy of Religion– Nature of Religion

● Why does religion exist?● Why are religions geographically distributed?● Why are there so many different religions

– Basic Questions● Does God exist?● What is the nature of God?● What evidence for God?

● Faith and Reason – Philosophy looks for reasons– Arguments not authority– Faith is not an argument

PHLA10S 4

The Five Ways of Aquinas

St. Thomas Aquinas (1225-1274)

● Aquinas’s God– Personal– Omnipotent– Omniscient– Omni-benevolent

● A Logical Problem– Can God make a stone so heavy

that He can’t lift it?– If so, then his power is limited.– If not, then his power is limited.– Are ‘logical limitations’ a genuine

limitation of God’s power?

PHLA10S 4

The Five Ways of Aquinas

● Way 1: Motion– Some objects move.– Any movement requires a cause.– Causes must come before their effects– An infinite chain of causes is impossible.– Therefore, there is a first cause of motion.– This first cause cannot be another moving body, so

it is something ‘outside’ the world – perhaps God.

PHLA10S 4

The Five Ways of Aquinas

● Way 2: General Causation– Some events occur.– No event occurs unless it has a cause.– Causes must occur before their effects.– An infinite chain of causes is impossible.– Therefore, there is a first event, Å.– Å must have a cause, but it cannot be another

event in the world.– Therefore there must be something outside the

world that causes the first event, perhaps 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. (from Aquinas’ Summa Theologica)

PHLA10S 4

Problems with the first 2 ways.

● Some premises are questionable.● Consider: Any movement requires a

cause.● Aristotelean vs. Newtonian physics

– Aristotle believed Aquinas’s premise.

– Not until Galileo/Newton was it shown to be false.

– Newton’s First Law:● A body at rest remains at rest,

and a body in motion continues to move in a straight line with a constant speed unless and until an external unbalanced force acts upon it.

Isaac Newton (1643-1727)

PHLA10S 4

Problems with the first 2 ways.

● Can we repair this problem?● Replace motion with acceleration.● Every change in motion of a body requires a cause.● But then, what about: causes must come before their

effects? – Is ‘backwards causation’ impossible?– Perhaps it is at least unlikely.

● What about Aquinas’s inference from ‘there is a cause outside nature’ to ‘the cause outside nature is God’?– How can we prove that the ‘outside cause’ has all

the features of God?

PHLA10S 4

Problems with the first 2 ways.

● The Birthday Fallacy– Aquinas assumes that this argument is valid:

● Every event has a cause.● Therefore, there is a cause of every event.

– Is this form valid?– Many counterexamples:

● Every person has a father.● Therefore, there is someone who is everyone’s

father.● Or, every wife has a spouse.● Therefore, there is someone who the spouse of

every wife.– So, why couldn’t there be a whole bunch of causes

of the events in our world instead of just one?

PHLA10S 4

Problems with the first 2 ways.

● Infinite Time– Aquinas uses the premise that there cannot be an

infinite chain of causes in the past.– Why not?– Arguments:

● If the universe is made of an infinite series of events, then we are at the end of an infinite series, but infinite series don’t have endpoints.

● What’s wrong with this?

Past times are like the negative numbers, with zero marking the present. – But what about the series as a whole? Does it need a cause?

PHLA10S 4

The Third Way

● Contingent and Necessary Beings– The contingent is what might not have existed.– The necessary is what must exist.

● Possible worlds:– Possible worlds are the different ways things could

have been● There is a possible world where the dinosaurs did

not go extinct.● There is a possible world where Germany won

the second world war.– You can think of possible worlds as corresponding to

long lists of sentences – the sentences that are true in that possible world.

G. W. Leibniz(1646-1716)

PHLA10S 4

The Third Way

● Using Possible Worlds, we can better understand contingency and necessity.– The necessary is what is true in every possible world.– Contingencies are what is true in only some of the

possible worlds.– Intuition check:

● If X is true, then X is possible.– If X is true then it is true in the actual world, so

it is true in some world, so it is possible.● If X is necessary then X is true.

– If X is necessary then it is true in every possible world, so it is true in the actual world, so it is true.

PHLA10S 4

The Third Way

● Aquinas’s Reductio ad Absurdem Argument – Suppose everything is contingent.– All contingent things come into and go out of

existence.– Therefore: there is a time when there are no

contingent things.– That time is in the past.– Therefore: there is a time when nothing exists.– But, if nothing exists at a time then nothing will ever

exist after that time.– So nothing would exist now!– That is absurd (plainly false) – so the original

assumption must be wrong. There is a non-contingent being.

– That would be God.

PHLA10S 4

The Third Way - Problems

● Almost every premise is doubtful.● Why must it be true that contingent things cannot be

eternal?● Even if all contingent beings eventually go out of

existence, why must there be a time when they are all non-existent? (What fallacy is that?)

● Even if there is time when all contingent go out of existence, why must that time be in the past?

● Is it certain that an empty world could not ‘generate’ things? (Conservation laws)

● Why would a non-contingent being be God?

PHLA10S 4

The Third Way - Problems

● A non-theological necessary being.– The number 2!– Abstract verus Concrete reality

● Truth and Being– Necessary true statements can entail existence– e.g. there is a prime number between 12 and 19

● Necessity versus Certainty– Necessity is objective– Certainty is subjective – one’s (or society’s) state of

belief in something● Are there any concrete necessary beings?

– If God is conceived as the creator of the universe, then He could not be an abstract object.

– Of course, that is no proof of anything, since we would need to know there was a creator for it to get a grip.

PHLA10S 4

The Third Way – A New Way?

● What about this argument:– Suppose that the universe is contingent.– Every contingent thing requires an explanation of why

it exists rather than not exist.– Therefore, the universe requires such an explanation.– Either that explanation involves further contingent

things or some necessary things.– If the former, then that explanation will require yet

another explanation to account for its contingency.– But there are no infinite explanatory regresses

(compare to the claim there are no infinite causal regresses).

– Therefore, their must be a necessary being which ultimately explains the contingent features of the world.