The course has been a tour of arguments. This lesson asks you to stop touring and stand somewhere, which is a different skill and the one the whole thing was for.
Holding a position is not the same as being confident. It means four things: saying what you think, saying which premise of the best argument against you that you deny, saying what your own view costs, and naming what would change your mind. A view that cannot do the fourth is not a position, it is an attachment.
The three arguments, in one page each
Everything in the course reduces to three valid arguments. Each is sound or unsound, and each position available to you is a choice about which premise to give up.
The sceptical argument. You do not know you are not a brain in a vat. If you know you have hands, then, since having hands entails not being a vat brain, you know you are not one. So you do not know you have hands.
Deny the first premise and you are with Moore or with the abductive reply of lesson four, holding that the external world is far and away the best explanation of experience and that this is what knowing amounts to. Deny the second and you are with Nozick, rejecting closure and accepting the abominable conjunction. Accept both and you are a sceptic, which almost nobody is, or a contextualist, holding that the argument is sound in the seminar and irrelevant outside it.
The design argument. The constants of physics fall in a narrow life-permitting range. That is very unlikely without a designer and likely with one. So the constants are evidence for a designer.
Deny the first premise by disputing the range, which is a live question in physics. Deny the second in either of two places: the denominator, by arguing that anthropic selection in an ensemble makes a life-permitting observation certain for any observer, which is lesson thirteen; or the numerator, by arguing that nobody has specified what a designer makes probable, which is lesson nine's demand that a hypothesis forbid something. Accept both and you have an argument for a designer, thin but real, which still has the distance problem of lesson ten.
The evidential problem of evil. There is suffering that an omnipotent, omniscient being could have prevented without losing a greater good. A perfectly good being would prevent such suffering. So no such being exists.
Deny the first with sceptical theism, at the price lesson nine named and lesson eleven spelled out. Deny the second with a theodicy, which requires an account that covers animal suffering and natural disaster rather than only moral evil. Accept both and you have a strong argument against the God of theism which leaves the deistic first cause standing.
Example. A reader says: "I am a naturalist. I think the physical world is all there is, it was not designed, and there is no God." Which premises are they committed to denying?
At least three, and they should know which. On the sceptical argument they need a reply, most naturally the abductive one, since a naturalist who cannot say why the external world is the better explanation has helped themselves to the physical world they are claiming exhausts reality. On the design argument they must deny a premise, and the honest choice is the denominator via anthropic selection, which as lesson thirteen showed commits them to an ensemble with real variation, which is a substantive bet on unsettled physics. On the contingency argument of lesson ten, which is not on the list above because the naturalist usually forgets it, they must either say the universe exists necessarily or accept a brute fact. Naming all three is what turns a mood into a position, and notice that two of the three cost something.
Now you. Do the same for someone who says: "I believe in God, and I accept everything science says."
Answer
Their commitments depend on which God, and that is the first thing to settle. If it is the deistic first cause, they are largely untroubled: the contingency argument supports them, the evidential problem of evil does not reach them as lesson eleven showed, and science is silent. If it is the omnipotent, omniscient, perfectly good God of theism, they must answer the evidential problem, which means either sceptical theism, with its cost of undermining the design argument they may also want, or a theodicy covering hundreds of millions of years of animal suffering. Accepting everything science says also means the Kalam is not available in its usual form, since cosmology does not deliver a beginning of existence, and it means evolution supplies the alternative to biological design. What remains available to them is strong: contingency, fine-tuning if they are willing to bet against the multiverse, and religious experience, which this course has not covered.
How to hold a view under uncertainty
Three habits, each of which is a lesson of this course compressed.
Keep credences rather than sides. You do not have to choose between certainty and paralysis. Lesson five's apparatus lets you say that the external world is overwhelmingly likely, that theism is somewhat unlikely, and that whether we are alone is close to unknown, and those three different attitudes are the correct response to three different evidential situations. Treating every question as though it demanded the same confidence is the error underneath most bad argument.
Apply your standards in both directions. This is the single most useful discipline the course offers and the rarest. If unfalsifiability is a defect when a theist appeals to inscrutable divine purposes, it is a defect when a physicalist explains away every apparent counterexample to physicalism. If a selection effect undercuts the fine-tuning argument, the same reasoning undercuts the optimistic reading of life arising early on Earth. Lesson six's point was not that your opponents are biased, it was that you are.
Distinguish what you believe from what you can show. Lesson twelve's agnostic atheist is the model: a low credence, held honestly, without the claim to have demonstrated anything. That combination is stable, defensible and much commoner among people who have thought hard than the public argument suggests.
Example. Two people agree on every argument in this course and end up with different views on theism. Is one of them making a mistake?
Not necessarily, and understanding why is the most grown-up thing in the lesson. Lesson five noted that Bayes tells you how to update and not where to begin. Two people who agree about the force of every argument can still differ in their priors, and priors are shaped by background commitments about what kinds of thing exist, which are themselves not settled by any of the arguments here. That is a real and respectable source of disagreement, and it is quite different from one party having missed a step. What it does not license is treating every disagreement as a difference in priors, which is a way of avoiding argument. The test is whether you can say what your prior is and why, and whether you would revise it under the conditions in the final section.
Now you. Someone says this means the whole subject is a matter of opinion. Why is that the wrong conclusion?
Answer
Because almost everything in the course was not a matter of opinion. That the sceptical argument is valid, that the free will defence answers the logical but not the evidential problem of evil, that the simulation argument concludes a disjunction, that anthropic selection makes an observation uninformative, that unfalsifiability yields no confirmation: all of these are results, and getting them wrong is getting something wrong. What remains genuinely open is a small residue, chiefly the priors, and it is much smaller than it looks from outside because most public disagreement is not about priors at all but about the results. The right description is that the subject narrows disagreement to a point and then leaves it there, which is exactly what a good philosophical education does and is why the point is worth reaching.
What would change your mind
Finish by writing the answer down, because it is the test of whether you have a position at all.
Some specimen answers, to show what a good one looks like. A physicalist should be moved by well-controlled evidence of mental causation without physical mechanism. An atheist should be moved by a successful theodicy covering natural evil, or by a demonstration that the space of possible physical constants is well defined and the life-permitting region is vanishingly small with no ensemble to draw from. A theist should be moved by a physical account of why the constants take the values they do, or by the multiverse becoming well confirmed for independent reasons. Someone confident we are alone should be moved by an independent origin of life on Mars or Europa, which as lesson fourteen noted would be bad news in another sense. Someone confident the universe is teeming should be moved by another fifty years of silence combined with better limits.
Notice what these have in common. Each is specific, each is at least conceivably obtainable, and none is "convincing evidence", which is not an answer but a refusal dressed as one.
If you cannot produce such a statement for your own view, that is worth knowing, and it does not mean the view is wrong. It means you hold it for reasons you have not articulated, which is the ordinary human condition and the thing fifteen lessons of this kind are meant to improve.
Example. Someone answers the question with: "I would change my mind about God if God appeared to me personally." Is that a good answer?
It is honest and nearly useless, for two reasons the course has covered. Lesson six explains why a private experience is weak evidence even to the person having it, since agency detection and motivated reasoning produce exactly such experiences whether or not anything is there, and the same person would presumably not accept someone else's private experience as evidence. And the answer sets a condition the answerer has no way to pursue, which makes it unfalsifiable in practice: nothing they could do would ever trigger it. A better answer names something public and at least approachable, such as a theodicy that handles animal suffering, or a specific result in cosmology. The test of a good answer is whether someone else could go and look.
Now you. What is the strongest objection to the position you now hold, and what is your answer to it?
Answer
There is no answer key here, and that is deliberate, but there is a way to check your own work. A good response names an argument from this course rather than a caricature, states it in the form its defenders would accept, and then denies a specific premise while acknowledging the cost. If your objection is one no serious opponent would make, you have picked the wrong one. If your reply is that the objection is obviously confused, you have almost certainly misread it, since every argument in this course is held by people who have thought about it longer than you have. And if you find you cannot state the strongest objection to your own view at all, that is the most useful result the course can give you, because it tells you exactly which lesson to read again.