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Philosophy of Religion
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Faith and Reason
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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
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The Five Ways of Aquinas
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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?
St. Thomas Aquinas (1225-1274)
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The Five Ways of Aquinas
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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.
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The Five Ways of Aquinas
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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)
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Problems with the first 2 ways.
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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)
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Problems with the first 2 ways.
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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?
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Problems with the first 2 ways.
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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 husband.
● Therefore, there is someone who the husband of
every woman.
– So, why couldn’t there be a whole bunch of causes
of the events in our world instead of just one?
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Problems with the first 2 ways.
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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.
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The Third Way
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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)
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The Third Way
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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.
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The Third Way
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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.
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The Third Way - Problems
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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?
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The Third Way - Problems
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A non-theological necessary being.
– The number 2!
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.
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The Third Way – A New Way?
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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.