Week 9 · Chapter

Chapter 9 — Philosophy of Religion

Introduction to Philosophy Free sample edition

The module's primary reading · ~45–55 minutes · Objective 5 (evaluate the classic arguments for and against the existence of God and the relationship between faith and reason), with Objective 2 (identify arguments, put them in standard form, judge whether they are valid, sound, or inductively strong, and test claims with counterexamples and thought experiments) and Objective 3 (explain central positions in metaphysics and epistemology — Plato's Forms, rationalism and empiricism, skepticism, and the analysis of knowledge — and evaluate the arguments for them) carried forward · Read it first this week; the lecture, the slide deck, the tutorial, the quiz, and the Philosophy Workshop all build on it.

In plain language

This week asks whether careful reasoning can show that God exists, or that God does not. You meet three classic arguments for God's existence: the ontological argument (an argument from the idea of a greatest possible being), the cosmological argument (an argument from the fact that things are caused), and the design argument (an argument from the order in nature). You also meet the strongest arguments on the other side, chiefly the problem of evil (the challenge that suffering poses for a wholly good, all-powerful God). Students of every belief, and of none, do the same work here: state each argument as its best defenders would, test it, and give the reply. The course does not tell you what to believe, and it keys no verdict on whether God exists.

Why you already care about this

A walker on a beach kicks something hard in the sand. It is a small brass machine, about the size of a fist, with gears that still turn and a dial that moves when you wind it. Nobody who found it would think the tide had built it. Someone, somewhere, made it, even if you never learn who.

Now picture a town after a flood. The river rose in the night, and by morning homes were gone and families were sleeping in a school gym. Many people there did nothing to bring the flood on. You may have heard someone ask, in a moment like that, how a good God could let it happen. You may have asked it yourself, or you may have heard someone answer it with care.

Those two scenes carry the two oldest questions in this part of philosophy. Does the order in the world point to a maker? And does the suffering in the world count against one? In 1802 William Paley wrote about a watch found on a heath. In 1955 J. L. Mackie argued that evil and a wholly good, all-powerful God cannot both exist. This chapter gives each side its strongest voice.

By the end of this chapter you will be able to:

define theism, atheism, and agnosticism, and sort an argument as a priori or a posteriori;
put Anselm's ontological argument in standard form and give the island objection and a reply;
state the cosmological argument from Aquinas's first three ways and give two objections and a reply;
reconstruct Paley's design argument as an argument from analogy and judge it for strength;
state Hume's two objections to the design argument and a reply from the design side;
show why Dataset B's argument 6 is invalid;
state the logical and evidential problems of evil, and the free will defense and soul-making replies;
explain why Pascal's wager is an argument about belief, not a proof.

Carry this line with you: Test an argument about God like any argument — not by who believes it.

Where we are

Already covered: Week 1, What Philosophy Is: Socrates and the Examined Life, taught you to test a claim by questioning it. Week 2, Arguments and Thought Experiments, gave you standard form, validity, inductive strength, and the valid and invalid forms. Week 3, Plato: Reality and the Forms, separated appearance from reality. Week 4, Knowledge I: Doubt, Reason, and Experience, set reason against experience. Week 5, Knowledge II: What Knowledge Is, gave you a priori and a posteriori. Weeks 6 and 7 asked what a mind is, what a self is, and whether you are free. Week 8, Midterm Review & Exam, reviewed Weeks 1 to 7 and introduced Pascal's wager.
This week: a new unit on God: the ontological, cosmological, and design arguments; Hume's objections; the logical and evidential problems of evil and the replies to them; and faith and reason, with the wager recalled.
How they connect: every argument this week is one you can put in standard form and test with Week 2's tools, and Week 5's a priori and a posteriori sort them into two kinds.
Where we're going next: Week 10, Ethics I: Relativism, God, and Self-Interest, begins the ethics unit and asks whether morality depends on God, on culture, or on self-interest.

Three tools from earlier weeks do most of the work. From Week 2, you need standard form: premises numbered P1, P2, and so on, the conclusion last, marked C and introduced by "So", and any premise the reconstruction adds marked "(added)". You need valid (the conclusion cannot be false if the premises are true) for deductive arguments and strength (how far true premises make the conclusion likely) for inductive ones. From Week 5, you need a priori (knowable without observation) and a posteriori (resting on observation). Week 2's forms come back too: denying the consequent is valid, and denying the antecedent is not.

1. Name the question: can reason settle it?

Picture two friends at a late-night diner. One believes in God, and the other does not. They have argued before, and it always ends with "you only believe it on faith" or "you refuse to look". Tonight they try something different: each one has to state the other's best argument so well that the other nods.

That is the spirit of this week. Here is the field in the course's words.

Philosophy of religion — the branch of philosophy that asks whether reason can show that God exists or does not, and how faith relates to reason.
Theism — the view that God exists; classical theism describes God as a being who is all-powerful, all-knowing, and wholly good.
Atheism — the view that God does not exist.
Agnosticism — the position of suspending judgment on whether God exists, holding neither that God exists nor that God does not.
Omnipotent — all-powerful: able to do anything that it is possible to do.

The arguments this week are about the God of classical theism. They do not compare or rank any religion, and they do not ask about any one tradition's teachings. They ask one question: can reason show that a being who is omnipotent, all-knowing, and wholly good exists, or does not?

Dataset G, the arguments about God, pins 6 standard arguments. Each has a source, a kind, and a direction.

Dataset G: six standard arguments about God, with each one's source, kind, and direction
Argument	Source	Kind	Direction
Ontological	Anselm, Proslogion (about 1077 to 1078)	a priori	for
Cosmological	Aquinas, Summa Theologica, the first three ways	a posteriori	for
Design	Paley, Natural Theology (1802)	a posteriori	for
The wager	Pascal, Pensées (1670)	prudential (about belief, not proof)	for belief
Hume's objections to the design argument	Hume, Dialogues Concerning Natural Religion (published after his death, 1779)	a critique of an a posteriori argument	against
Problem of evil	Mackie (1955), logical version	logical (inconsistency) or evidential (probability)	against

Read the table as a map, not a scoreboard. Each argument has serious defenders and serious critics. The kind column uses Week 5's distinction: an a priori argument starts from ideas alone, and an a posteriori argument starts from what we observe.

Misconception check — arguing about God is not attacking anyone's faith. Students often think that testing an argument for God is a way of saying belief is foolish, or that testing an argument against God is a way of saying unbelief is. It is tempting because the question matters so much to so many people. The cure is the diner. Stating an argument fairly and testing its premises is a form of respect. A believer can find an argument for God weak and stay a believer; an atheist can find an argument against God weak and stay an atheist.

2. State the ontological argument from an idea

Think of the greatest pizza you can imagine. Now imagine that same pizza, but one that actually exists, hot, on the table in front of you. Which is greater, the pizza in your head or the one on the table? Most people say the real one. Hold on to that thought.

Anselm, in his Proslogion (written about 1077 to 1078), turned that thought into an argument about God.

Ontological argument — an a priori argument for God's existence, given by Anselm in his Proslogion, that reasons from the idea of a being than which nothing greater can be conceived to the conclusion that such a being exists in reality.

Here is the argument in its strongest form. Start with what the word "God" means: a being than which nothing greater can be conceived. Anyone who hears that phrase understands it, so the being exists at least in the understanding, as an idea. But a being that exists in reality, too, is greater than one that exists only as an idea. So if this being existed only as an idea, you could conceive of a greater one, the same being, existing in reality. That would mean you could conceive of something greater than the being than which nothing greater can be conceived, which cannot be. So the being exists in reality.

Worked example — the ontological argument in standard form. This is the course's reconstruction (illustrative), written to teach the steps. P3 is a premise the reconstruction adds, so it is marked.

P1: God is a being than which nothing greater can be conceived.

P2: This being exists at least in the understanding, since anyone who hears the phrase understands it.

P3 (added): If this being existed only in the understanding, a greater being could be conceived: the same being, existing in reality too.

P4: Nothing greater than a being than which nothing greater can be conceived can be conceived.

C: So God exists in reality, not only in the understanding.

Now judge it. Look at P3 and P4 together. P3 says: if the being existed only in the understanding, a greater being could be conceived. P4 says a greater being cannot be conceived. That is the pattern if P then Q; not Q; so not P, which is denying the consequent. So the being does not exist only in the understanding. P2 says it exists in the understanding at least, so it exists in reality as well. Read this way, the argument is valid: if all four premises are true, C cannot be false.

In one plain sentence: Anselm's argument claims that the idea of the greatest conceivable being is the idea of a being that must exist, so denying that it exists ends in a contradiction.

Misconception check — the ontological argument is a priori. Students often think every argument for God must start from something in the world, a sunset or a miracle. It is tempting because most arguments we meet do start from evidence. The cure is to look at the premises. None of P1 to P4 reports an observation. Each is about an idea and what follows from it. That makes the argument a priori, which is why Dataset G sorts it that way.

3. Press the ontological argument with an island

Picture a travel website advertising "the greatest possible island": perfect beaches, perfect weather, perfect fruit on every tree. It is a lovely idea. Does the idea prove the island is out there in the ocean somewhere?

Here is the most famous objection, in the course's words.

Greatest-possible-island objection — the objection to the ontological argument that the same pattern of reasoning would prove that a greatest possible island exists, which shows that something must be wrong with the pattern.

Worked example — the island run through the same pattern. Swap "island" for "being" and keep everything else.

P1: The greatest possible island is an island than which no greater island can be conceived.
P2: This island exists at least in the understanding.
P3 (added): If it existed only in the understanding, a greater island could be conceived: the same island, existing in reality too.
P4: No island greater than the greatest possible island can be conceived.
C: So the greatest possible island exists in reality.

The conclusion is plainly false; no such island is on any map. The pattern looks the same. So, the objection says, something in the pattern must be wrong, even if we cannot yet say which premise it is.

The reply, from the argument's side: the island case is not a fair copy. An island has no greatest possible form. However good an island is, you can always imagine one more beach, one more tree, one more perfect sunset. So "the greatest possible island" picks out nothing. A being than which nothing greater can be conceived is different. It is the one case where the idea itself fixes a maximum, so the pattern works only there.

Here is a caveat worth keeping. A second objection, also still argued over, asks whether existing really makes a thing greater, or whether "exists" only says that the idea is true of something. Both objections, and the replies to them, are open questions, and the course keys no verdict on them.

Misconception check — a parody is not a refutation. Students often think that once the island is on the table, the ontological argument is finished. It is tempting because the parody is funny and quick. The cure is to read the reply. An objection by parallel argument works only if the parallel is truly parallel. Whether the island is a fair copy is exactly what the two sides dispute.

4. State the cosmological argument from Aquinas's first three ways

Line up a long row of dominoes and tip the first one. Each domino falls because the one before it hit it. Now suppose you walk along the row and find every domino lying flat. You would ask what started it. A row of falling dominoes, each pushed by the one before, does not seem able to explain itself.

That is the thought behind a second argument, which starts from the world rather than from an idea. Thomas Aquinas's Summa Theologica, First Part, Question 2, Article 3, opens its proofs with this sentence. The translation is by the Fathers of the English Dominican Province:

"The existence of God can be proved in five ways."

These English words are the translators', not Aquinas's own. He wrote in Latin.

The five ways — the arguments Thomas Aquinas gives in his Summa Theologica for the existence of God; the first three argue from change, from causes, and from things that might not have existed, and the fifth is a design argument.
Cosmological argument — an a posteriori argument for God's existence that starts from observed facts, such as that things change, are caused, or might not have existed, and argues that there must be a first cause or a being that could not fail to exist.
First cause — a cause that nothing else causes, at which a chain of causes would stop; the cosmological argument concludes that one exists.

Worked example — counting the ways. Aquinas gives 5 ways. The first 3 are the cosmological argument. So 5 − 3 = 2 ways remain, the fourth and the fifth, and the fifth is a design argument. In words: three of the five ways are this week's cosmological argument, and one of the two left over is a cousin of the design argument you meet in section 6.

Here is the way from causes in its strongest form. We observe that things are caused to exist: a tree by a seed, a seed by a tree. Nothing causes itself, since it would have to exist before it exists to do so. And a chain of causes cannot go back forever, because then nothing would get the chain started. So there must be a first cause, which nothing else causes.

Worked example — the way from causes in standard form. This is the course's reconstruction (illustrative).

P1: Some things are caused to exist.

P2: Nothing is the cause of itself, either directly or through a loop of other causes.

P3: A chain of causes cannot go back forever.

C: So there is a first cause that nothing else causes.

Now judge it. Take anything that is caused, as P1 says some things are. Its cause is something else (P2), and that cause's cause is something else again, with no loops (P2). The chain cannot go back forever (P3). So it must stop somewhere, at a cause that nothing else causes. The argument is valid as reconstructed: if all three premises are true, every chain of causes stops at a first cause.

Notice the kind. P1 is something you learn by looking at the world. That makes the cosmological argument a posteriori, the opposite of Anselm's.

Misconception check — the cosmological argument does not say "everything has a cause". Students often state the argument as "everything has a cause, so God caused everything," and then ask what caused God. It is tempting because the shorter slogan is easy to remember. The cure is P1 and P2. The argument says that some things are caused and that nothing causes itself. Its conclusion is a first cause that nothing else causes, so "what caused it?" is the question the argument says has no answer.

5. Press the cosmological argument, then reply

Think again about the dominoes. Could the row go on forever, with no first domino at all? Picture a row stretching back past every horizon. Each domino would still be explained by the one before it. Is anything left over to explain?

That is the first objection. The second asks about the conclusion. Suppose the argument shows there is a first cause. Why should that first cause be wholly good, or all-knowing, or a person at all? A first cause might be some basic physical event. Critics sometimes call this the gap between "a first cause" and "God".

Worked example — two objections and a reply, laid out. Each line names its target first.

Objection to P3: a chain of causes might go back forever. Each link would then be explained by an earlier link, and no first cause would be needed.
Objection to the step from C to God: a first cause need not be wholly good or all-knowing, so the argument, even if it works, may not reach the God of classical theism.
Reply, from the argument's side, to the first: the chain at issue is one of causes acting now, at once, like a hand that moves a stick that moves a stone. The stone moves only while the stick moves, and the stick moves only while the hand moves. A chain like that, with no first mover, would be all sticks and no hand, and nothing would move.
Reply, from the argument's side, to the second: the argument aims to show only that a first cause exists. Its defenders argue for the first cause's other qualities in further steps.

In one plain sentence: the cosmological argument says that a chain of causes must start with a first cause, and the two sides dispute whether the chain could go back forever.

Misconception check — an objection to one premise is not a verdict. Students often think that once someone imagines a chain going back forever, the argument is refuted. It is tempting because the image is easy to picture. The cure is the hand and the stick. The two sides disagree about what kind of chain the argument is about, and that disagreement is still open.

6. Find the watch on the heath

Now the week's thought experiment, the Week 9 case on the course's thought-experiment roster.

William Paley's Natural Theology (1802) asks you to imagine crossing a heath, an open stretch of rough, wild land, and striking your foot against a stone. You would not wonder how it came to be there. Now imagine finding a watch on the ground instead. You open it and see springs, wheels, and a spring-driven train of gears, all fitted together so that the hands mark the hours. You would conclude, Paley argues, that the watch had a maker.

The watch on the heath — William Paley's case from Natural Theology of 1802, in which a watch found on a heath shows a watchmaker, used to ask whether the order of living things shows a designer.
Design argument — an a posteriori argument for God's existence that starts from the order of the world, such as parts that fit together to serve a purpose, and argues that this order shows a designer.

Paley argues by analogy that, as a watch found on a heath shows a watchmaker, the order of living things shows a designer. His favorite examples are living things, such as the eye, whose parts fit together to let a creature see.

The roster gives the case a question: Does order show a designer? It tests the design argument. The brass machine on the beach from the start of this chapter is a variation on Paley's case, written for this course: same shape, different place.

Misconception check — the design argument is not the cosmological argument. Students often think these are one argument, because both conclude that something made the world. It is tempting because both are a posteriori and both point to a maker. The cure is to look at where each one starts. The cosmological argument starts from the bare fact that things exist, change, or are caused. A row of identical stones would be enough for it. The design argument starts from order: parts fitted together for a purpose. A pile of random stones would give it nothing to work with.

7. Judge the design argument for strength, then meet Hume

Think of two houses on one street with the same roof shape, the same windows, and the same odd blue door. You might guess that the same builder made both. You would not be certain, but the likeness gives your guess some support. That is reasoning by analogy.

Argument from analogy — an inductive argument that reasons from the ways two things are alike to the conclusion that they are probably alike in a further way; it is judged for strength, not validity.

Worked example — the design argument in standard form. This is the course's reconstruction (illustrative). P3 is added, so it is marked.

P1: A watch, whose parts fit together to serve a purpose, has a designer.

P2: Living things, such as an eye, have parts that fit together to serve a purpose, as a watch's do.

P3 (added): Things alike in this way are probably alike in having a designer.

C: So living things probably have a designer.

Now judge it. The word "probably" tells you this is an inductive argument, an argument from analogy. You do not ask whether it is valid. You ask how strong it is, and the strength depends on how close the analogy is. The more an eye is like a watch in the ways that matter, the stronger the argument.

Here is where David Hume comes in. Hume's Dialogues Concerning Natural Religion (published after his death, 1779) press the design argument on 2 fronts:

First, the analogy is weak. The universe is not much like a machine. It is at least as much like a plant or an animal, things that grow from within rather than being built from outside.
Second, order would not show a single, perfect, or still-living designer. A ship may be built by a whole crew of workers, and a flawed machine by a clumsy one, and a builder may die after the job is done. So even if order shows some designer, it does not show one who is single, perfect, and still living.

Worked example — the timeline. Hume's Dialogues came out in 1779. Paley's Natural Theology came out in 1802. The gap: 1802 − 1779 = 23 years. In words: Hume's objections were in print 23 years before Paley's watch, so Paley wrote with the objections already on the table.

The reply, from the design side: an analogy need not be perfect to give some support. The eye and the watch are alike in the very feature that matters, parts fitted together to serve a purpose. And the argument claims only a designer. Whether the designer is single, perfect, and still living needs further argument, which defenders of the design argument try to supply.

In one plain sentence: the design argument reasons by analogy from order to a designer, and Hume replies that the analogy is weak and the conclusion too large for the evidence.

Misconception check — an inductive argument is not "invalid". Students often say the design argument is invalid because its conclusion could be false. It is tempting because Week 2 taught you to hunt for invalid forms. The cure is the word "probably". An argument from analogy never claims that its conclusion must be true. It is judged by a different standard, strength, so calling it invalid misreads what kind of argument it is.

8. Check a tempting argument

Picture a student in a late-night study group who has read Hume and is excited. They reason like this. The argument is from Dataset B, the argument set (illustrative); its premises were written for teaching, and the course does not endorse them.

Worked example — Dataset B, argument 6, in standard form. Lay it out, then check the form.

P1: If the universe was designed, it shows order.

P2: The universe was not designed.

C: So it shows no order.

Let P be "the universe was designed" and Q be "it shows order". The pattern is if P then Q; not P; so not Q. That is denying the antecedent, from Week 2. Key it: invalid.

Here is the counterexample, using Week 2's method. Keep the pattern, change the content: "If this garden was planted by a gardener, it has flowers. This garden was not planted by a gardener. So it has no flowers." A wild meadow full of flowers makes both premises true and the conclusion false. The same goes for the universe: order could come from some other source, so both premises could be true while the conclusion is false.

Misconception check — an invalid argument is not a point for the other side. Students often think that because argument 6 is invalid, the universe must have been designed. It is tempting because the argument was aimed against design. The cure is Week 2's rule. An invalid argument fails to support its conclusion; it does not show that the opposite is true. Argument 6 tells you nothing either way about design.

9. State the problem of evil

Back to the town after the flood. A nurse at the shelter in the school gym has worked all night. A child has a fever, an older couple has lost their home of forty years, and no one there did anything to deserve it. Someone asks the question out loud: if God is wholly good and all-powerful, why did this happen?

That question is the best-known argument against God's existence in the classic debate.

Problem of evil — the argument that the evil and suffering in the world count against the existence of a God who is wholly good and all-powerful; it comes in a logical and an evidential version.
Logical problem of evil — the version of the problem of evil, pressed by J. L. Mackie in 1955, which claims that the existence of evil is logically inconsistent with the existence of a God who is wholly good and omnipotent.
Evidential problem of evil — the version of the problem of evil which claims that the amount and kind of suffering in the world make God's existence unlikely, rather than impossible.

J. L. Mackie, in "Evil and Omnipotence" (Mind, 1955), argues that the existence of evil is logically inconsistent with the existence of a God who is wholly good and omnipotent. Here is the argument in its strongest form. A wholly good being would want to prevent evil. An omnipotent being could prevent it. So if such a being existed, there would be no evil. But there is evil.

Worked example — the logical version in standard form. This is the course's reconstruction (illustrative). P2 is added, so it is marked.

P1: If a wholly good, omnipotent God exists, God wants to prevent all evil and is able to.

P2 (added): Whatever wants to prevent all evil and is able to leaves no evil.

P3: Evil exists.

C: So a wholly good, omnipotent God does not exist.

Now judge it. P1 and P2 chain together. If such a God exists, God wants to and is able to prevent all evil, and whatever wants to and is able to leaves no evil. So if such a God exists, there is no evil. That is a hypothetical syllogism. P3 then denies the consequent, "there is no evil". So C follows. The argument is valid: if all three premises are true, C cannot be false.

The evidential version is a different kind of argument. It does not claim that God and the flood's suffering cannot both exist. It claims that the amount and kind of suffering, such as a child's fever in a shelter after a flood no one caused, make God's existence unlikely. That makes it an inductive argument, judged for strength, like the design argument.

Worked example — the timeline, continued. Paley's Natural Theology came out in 1802 and Mackie's paper in 1955. The gap: 1955 − 1802 = 153 years. In words: the logical problem of evil, in Mackie's form, was published 153 years after Paley's watch, though the question it asks is far older.

Misconception check — the problem of evil is not an argument that religious people are bad. Students often hear "the problem of evil" and think it accuses believers of something, or says religion causes harm. It is tempting because the word "evil" sounds like a charge against someone. The cure is to read the premises. The argument is about whether a set of claims fits together, that God is wholly good, that God is omnipotent, and that evil exists. It says nothing about the character of anyone who believes in God.

10. Weigh the responses: free will and soul-making

Picture a parent teaching a teenager to drive. The parent could keep the car in the driveway forever, and the teenager would never crash. But the teenager would never learn to drive either, and would never become a careful driver by their own choices. Some goods seem to come only with some risk.

That is the thought behind the two best-known responses to the problem of evil. First, two terms that sort the harms in the flood town.

Moral evil — harm that comes from the free choices of people, such as cruelty or theft.
Natural evil — harm that comes from natural events rather than from anyone's choice, such as the suffering a flood or an earthquake causes.

Now the responses.

Free will defense — a response to the problem of evil which holds that a world with free creatures is better than one without them, and that even an all-powerful being cannot make creatures who are free yet certain always to choose well.
Theodicy — an attempt to give the reasons a wholly good, all-powerful God would have for allowing evil.
Soul-making theodicy — a theodicy which holds that hardship and suffering give people the chance to grow in virtues such as courage and compassion, which they could not develop in a world without them.

Worked example — the free will defense against P1. Follow where the defense aims.

Its target: P1 of the logical version, that a wholly good, omnipotent God wants to prevent all evil and is able to.
On "wants to": a wholly good God might allow some evil if preventing all of it would cost a greater good, a world of free creatures who can choose good for themselves.
On "is able to": omnipotence means being able to do anything it is possible to do. Making creatures who are free yet certain always to choose well may not be possible, as a square circle is not, so even an omnipotent God could not do it.
What follows: if P1 is false, the logical version's conclusion no longer follows, and God and evil caused by free choices may be consistent after all.

The reply, from the critic's side: the flood is natural evil. No one chose it. So the free will defense does not cover it by itself. A soul-making theodicy may help there, since the shelter is also where the nurse's compassion and the neighbors' courage showed. But the evidential version presses on: is this much suffering, including a child's, needed for any good?

In one plain sentence: the free will defense and the soul-making theodicy each name a greater good that evil might serve, and critics answer that natural evil and the amount of suffering remain.

Here is an honesty note. These responses, and the replies to them, are still argued over by careful thinkers of every belief, and the course keys no verdict on whether any of them succeeds.

Misconception check — a defense is not a claim that suffering is good. Students often think the free will defense or the soul-making theodicy says that suffering does not matter, or that people in the flood deserved it. It is tempting because "a reason God allows evil" can sound cold. The cure is to read what each response claims. Each says that allowing some evil might serve a greater good; neither says the suffering is not real, not bad, or deserved.

11. Recall the wager, and name faith and reason

Think of someone deciding whether to bring an umbrella on a cloudy morning. They cannot prove it will rain. But carrying an umbrella costs little, and getting soaked costs more, so they bring it. That is a decision about what to do under uncertainty, not a proof about the weather.

In Week 8 you met an argument with that shape. Blaise Pascal, in his Pensées (published after his death, in 1670), argues that since the possible gain from believing in God is infinite and the possible loss finite, a prudent person should wager that God exists. Dataset G sorts the wager by kind as prudential, about belief rather than proof, and by direction as "for belief", not "for God's existence". It is an argument about what to believe, not a proof that God exists.

That raises the last question of the week: how do faith and reason relate? Two broad views stand out.

Natural theology — the project of arguing for God's existence from reason and from observation of the world, without appeal to revelation or scripture.

On the first view, belief in God should rest on argument and evidence, the project that the ontological, cosmological, and design arguments carry out and that Paley's title, Natural Theology, names. On the second view, faith can go beyond what argument shows. A person may hold a belief by faith while granting that no argument proves it, as many people trust a friend beyond what the evidence alone would show. Each view has thoughtful defenders. Each also has critics: the first must answer Hume and the problem of evil, and the second must say when believing beyond the evidence is reasonable.

Misconception check — the wager is not a proof that God exists. Students often remember the wager as "Pascal's proof of God". It is tempting because it appears in the same debates as the ontological and cosmological arguments. The cure is Dataset G's direction column. The wager is "for belief", not "for" God's existence: it argues that believing is the prudent bet, and it gives no reason to think the bet will pay.

12. Weigh the six arguments side by side

You now have all 6 arguments of Dataset G in hand. The fair way to compare them is the course's way: each one in its strongest form, its strongest objection, and a reply from its own side.

The ontological, cosmological, and design arguments and the problem of evil compared: central claim, strongest objection, and a reply
Argument	Central claim	Strongest objection	Reply from its side
Ontological	The idea of the greatest conceivable being is the idea of a being that must exist.	The greatest possible island: the same pattern would prove too much.	An island has no greatest possible form; a greatest conceivable being does.
Cosmological	A chain of causes must start with a first cause.	The chain might go back forever, and a first cause need not be God.	The chain at issue is of causes acting now; the other qualities need further argument.
Design	Order, as in a watch or an eye, shows a designer.	Hume: the analogy is weak, and order would not show a single, perfect, or still-living designer.	A partial analogy still gives support; the designer's qualities need further argument.
Problem of evil	Evil is inconsistent with, or makes unlikely, a wholly good, omnipotent God.	The free will defense and soul-making theodicies.	Natural evil and the amount of suffering remain.

Worked example — counting Dataset G's direction column. Count each direction.

For God's existence: 3 (ontological, cosmological, design).
For belief: 1 (the wager).
Against: 2 (Hume's objections and the problem of evil).
In all: 3 + 1 + 2 = 6 arguments.

In words: Dataset G holds 6 arguments, and only 3 of them aim to prove that God exists, which is why the wager and Hume's objections each need their own label.

Where do the two sides disagree, in one plain sentence? Defenders of the three arguments for hold that reason, starting from an idea or from the world, can show that God exists. Critics hold that Hume's objections and the problem of evil show that reason cannot reach such a God, or even counts against one.

A limitation to keep in view: this week covers only the classic arguments, and the course keys no verdict on whether God exists. Your job is to state each argument so well that its own defenders would sign it.

Pause and think, choosing one of these two options:

(a) Pick the argument for God's existence you find strongest, and write two sentences giving its strongest objection and the best reply you can find.
(b) Pick the argument against God's existence you find strongest, and write two sentences giving the best response a theist could make and how a critic would answer it.

Misconception check — a count is not a score. Students often think that because Dataset G has 3 arguments for God's existence and 2 against, the "for" side is winning. It is tempting because counting feels objective. The cure is to remember what the table counts: how many classic arguments there are, not how good they are. One sound argument would settle the question, and that is exactly what is in dispute.

Key terms

Philosophy of religion — The branch of philosophy that asks whether reason can show that God exists or does not, and how faith relates to reason. (first used: 1. Name the question: can reason settle it?)
Theism — The view that God exists; classical theism describes God as a being who is all-powerful, all-knowing, and wholly good. (first used: 1. Name the question: can reason settle it?)
Atheism — The view that God does not exist. (first used: 1. Name the question: can reason settle it?)
Agnosticism — The position of suspending judgment on whether God exists, holding neither that God exists nor that God does not. (first used: 1. Name the question: can reason settle it?)
Omnipotent — All-powerful: able to do anything that it is possible to do. (first used: 1. Name the question: can reason settle it?)
Ontological argument — An a priori argument for God's existence, given by Anselm in his Proslogion, that reasons from the idea of a being than which nothing greater can be conceived to the conclusion that such a being exists in reality. (first used: 2. State the ontological argument from an idea)
Greatest-possible-island objection — The objection to the ontological argument that the same pattern of reasoning would prove that a greatest possible island exists, which shows that something must be wrong with the pattern. (first used: 3. Press the ontological argument with an island)
The five ways — The arguments Thomas Aquinas gives in his Summa Theologica for the existence of God; the first three argue from change, from causes, and from things that might not have existed, and the fifth is a design argument. (first used: 4. State the cosmological argument from Aquinas's first three ways)
Cosmological argument — An a posteriori argument for God's existence that starts from observed facts, such as that things change, are caused, or might not have existed, and argues that there must be a first cause or a being that could not fail to exist. (first used: 4. State the cosmological argument from Aquinas's first three ways)
First cause — A cause that nothing else causes, at which a chain of causes would stop; the cosmological argument concludes that one exists. (first used: 4. State the cosmological argument from Aquinas's first three ways)
The watch on the heath — William Paley's case from Natural Theology of 1802, in which a watch found on a heath shows a watchmaker, used to ask whether the order of living things shows a designer. (first used: 6. Find the watch on the heath)
Design argument — An a posteriori argument for God's existence that starts from the order of the world, such as parts that fit together to serve a purpose, and argues that this order shows a designer. (first used: 6. Find the watch on the heath)
Argument from analogy — An inductive argument that reasons from the ways two things are alike to the conclusion that they are probably alike in a further way; it is judged for strength, not validity. (first used: 7. Judge the design argument for strength, then meet Hume)
Problem of evil — The argument that the evil and suffering in the world count against the existence of a God who is wholly good and all-powerful; it comes in a logical and an evidential version. (first used: 9. State the problem of evil)
Logical problem of evil — The version of the problem of evil, pressed by J. L. Mackie in 1955, which claims that the existence of evil is logically inconsistent with the existence of a God who is wholly good and omnipotent. (first used: 9. State the problem of evil)
Evidential problem of evil — The version of the problem of evil which claims that the amount and kind of suffering in the world make God's existence unlikely, rather than impossible. (first used: 9. State the problem of evil)
Moral evil — Harm that comes from the free choices of people, such as cruelty or theft. (first used: 10. Weigh the responses: free will and soul-making)
Natural evil — Harm that comes from natural events rather than from anyone's choice, such as the suffering a flood or an earthquake causes. (first used: 10. Weigh the responses: free will and soul-making)
Free will defense — A response to the problem of evil which holds that a world with free creatures is better than one without them, and that even an all-powerful being cannot make creatures who are free yet certain always to choose well. (first used: 10. Weigh the responses: free will and soul-making)
Theodicy — An attempt to give the reasons a wholly good, all-powerful God would have for allowing evil. (first used: 10. Weigh the responses: free will and soul-making)
Soul-making theodicy — A theodicy which holds that hardship and suffering give people the chance to grow in virtues such as courage and compassion, which they could not develop in a world without them. (first used: 10. Weigh the responses: free will and soul-making)
Natural theology — The project of arguing for God's existence from reason and from observation of the world, without appeal to revelation or scripture. (first used: 11. Recall the wager, and name faith and reason)

Summary

The philosophy of religion asks whether reason can show that God exists or does not.
Anselm's ontological argument is a priori; read as reconstructed, it is valid by denying the consequent.
The island objection says the same pattern would prove too much; the reply says an island has no maximum.
Aquinas's first three ways are the cosmological argument, an a posteriori argument to a first cause.
The design argument starts from order, so it is not the cosmological argument.
Paley's watch on the heath (1802) is an argument from analogy, judged for strength, not validity.
Hume's objections: the analogy is weak, and order would not show a single, perfect, or still-living designer.
Dataset B's argument 6 is invalid, because it denies the antecedent.
The logical problem of evil (Mackie, 1955) claims inconsistency; the evidential version claims improbability.
The free will defense targets moral evil; natural evil is the critic's reply.
Pascal's wager is an argument about what to believe, not a proof.
No argument is keyed as sound; whether God exists stays an open question.

Check your understanding

Work these before looking at the answers — they are ungraded, and the answers (with reasoning) are at the bottom of the page.

Sort each argument as a priori or a posteriori, and say which of this week's arguments it is most like: (a) "Every event in this lab notebook has a recorded cause, so the chain of causes must start somewhere." (b) "A perfect being must exist, since the very idea of a perfect being includes existing." (c) "This hummingbird's beak fits its flower so exactly that it must have been planned."
A baker says, "If the oven was preheated, the bread will rise. The oven was not preheated. So the bread will not rise." Put the argument in standard form, name its form, and say whether it is valid.
A classmate writes, "The problem of evil proves that people who believe in God are bad people." Explain what is wrong with that sentence, and rewrite it so it states the argument fairly.
A volunteer at a relief center lists three harms: (a) a wildfire started by lightning, (b) a scammer who empties an elderly neighbor's savings, (c) a drought that ruins a harvest. Sort each as moral evil or natural evil, and say which one the free will defense speaks to most directly.

Answers (worked reasoning — read after attempting)

(a) A posteriori, and most like the cosmological argument: it starts from observed causes and argues back to a first one. (b) A priori, and most like the ontological argument: it starts from an idea alone, with no observation. (c) A posteriori, and most like the design argument: it starts from order, parts fitted to a purpose, and argues to a planner by analogy.
P1: If the oven was preheated, the bread will rise. P2: The oven was not preheated. C: So the bread will not rise. Let P be "the oven was preheated" and Q be "the bread will rise". The pattern is if P then Q; not P; so not Q, which is denying the antecedent. That form is invalid: dough can rise from its yeast in a warm kitchen whether or not the oven was preheated, so both premises can be true while the conclusion is false.
The argument says nothing about anyone's character. It asks whether three claims fit together: that God is wholly good, that God is omnipotent, and that evil exists. A fair version: "The logical problem of evil argues that the existence of evil is inconsistent with the existence of a God who is wholly good and omnipotent."
(a) Natural evil: lightning is a natural event, not anyone's choice. (b) Moral evil: the harm comes from a person's free choice to steal. (c) Natural evil: a drought is a natural event. The free will defense speaks most directly to (b), because it explains evil that comes from free choices; (a) and (c) are the cases critics press against it.

Next up in this module: the Readings & Resources page, the lecture tutorial, the practice set, the quiz, the discussion, and the assignment. Next week, the Euthyphro dilemma tests divine command theory, the view that morality depends on God.

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