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8 threads that run across the year rather than belonging to one school. Each lists all its lessons, 138 in all, with the week it comes in. Anyone can read a lesson.

Foundation · 13 lessons

What it means to know something, and why your own life is worth examining.

The Examined Life · Week 1
A belief is worth keeping when you can say what would count against it.
Socratic Ignorance · Week 1
Before you say “obviously,” ask what the obvious part is.
Leaving the Cave · Week 1
What you usually see may be only shadows; ask what a different light would show.
Define the Word · Week 1
Many quarrels are two meanings under one word; name the test you mean.
The Ship of Theseus · Week 1
“Same” can mean same parts, same history or same use; say which one you mean.
The Map Is Not the Territory · Week 1
A model is a useful summary, not the thing itself; let the walk correct the map.
A Reason to Believe · Week 33
A lucky true guess is not knowledge; you need a reason that connects to the truth.
Luck Is Not Knowledge · Week 33
Check that your reason is what actually makes the belief true.
Are You the Same Person? · Week 37
What makes you the same person across time may be continuity, not a hidden core.
The Teleporter · Week 37
Parfit argued that personal identity is not what matters; what matters is the continuity of memory, character and plans.
Free Will and Causes · Week 37
Being free may mean acting on your own reasons, even though your reasons have causes.
Laplace’s Demon · Week 37
If the past and the laws fix everything, are your choices up to you? And if nothing fixes them, are they just chance?
Could You Have Done Otherwise? · Week 37
Frankfurt argued you can be responsible without being able to do otherwise; Strawson grounded blame in our feelings.

Critical thinking · 38 lessons

Arguments, fallacies and the discipline of stating the other side fairly.

Deduction and Induction · Week 3
A deduction’s conclusion must be true if its premises are; an induction only makes its conclusion likely.
Ad Hominem · Week 3
Answer the claim, not the person making it.
You Too · Week 3
Pointing out that a speaker does the same does not answer what the speaker said.
The False Dilemma · Week 3
Two choices are often a menu with options left off; name a third.
The Slippery Slope · Week 3
A warning about “the next step” must show what forces that step.
Natural Means Good? · Week 3
Natural does not mean safe or good, and artificial does not mean harmful.
Everyone Says So · Week 3
How many people believe a claim does not show it is true; ask what they are basing it on.
Off the Scent · Week 3
A reply can be true and still not answer the question; after any reply, check that the first question was answered.
Old Is Not Proof · Week 3
A practice is not right just because it is old; ask what it was for and whether that reason still holds.
Chance Has No Memory · Week 4
A fair coin does not keep score: after a run of heads, the next toss is still an even bet.
Sunk Costs · Week 4
What you have already spent is gone either way; decide by what lies ahead.
True Whether You Like It · Week 4
Whether a claim is true and whether you would like it to be true are separate questions.
Steelmanning · Week 5
State the other side so well that its owner would sign it, then answer that.
Going in Circles · Week 7
If a reason only works on people who already believe the conclusion, it is doing no work.
Moving the Goalposts · Week 7
Agree in advance what would count as evidence, so the test cannot be changed after it is passed.
Loaded Questions · Week 7
A question can carry a hidden claim inside it, and answering it accepts the claim.
Valid or Just Familiar? · Week 7
“If A then B, and B, so A” feels right but does not follow.
One Word, Two Meanings · Week 7
An argument can slide between two senses of a word, and the conclusion only works in one.
When Feelings Do the Arguing · Week 7
Feelings can show what is at stake, but they cannot stand in for the reasons.
No True Scotsman · Week 7
When a counterexample appears, weaken the claim instead of redefining the group to shut it out.
Occam’s Razor · Week 13
Prefer the explanation with fewer unsupported parts, and test it.
A Weak Analogy · Week 13
A good analogy shares the feature the conclusion needs; a weak one only looks alike.
Shifting Ground · Week 13
Watch for a bold claim that retreats to a safe one when challenged, then advances again.
The Whole and Its Parts · Week 13
What is true of a group is not always true of each member, and the reverse also holds.
When Authority Counts · Week 13
Trust trained agreement over fame, and treat an expert’s word as a place to start checking.
Necessary and Sufficient · Week 13
Needed is not the same as enough.
Except for Me · Week 13
To earn an exception, show what sets your case apart in a way the rule cares about; wanting one is not enough.
If-Then and Its Two Safe Moves · Week 13
From “if A then B,” affirm A to get B, or deny B to get not-A; those two moves are safe.
The Contrapositive · Week 13
“If A then B” says the same as “if not B then not A,” and nothing about the other two turns.
All and Some · Week 13
“All A are B” places any A among the B; it cannot be turned around, and one exception breaks it.
Either-Or and the Reductio · Week 13
Ruling out one option leaves the other if the list was complete; assuming a claim and hitting a contradiction rules the claim out.
Only If, and If and Only If · Week 13
“A only if B” points one way; “A if and only if B” points both ways; many quarrels about rules are about which was meant.
Expected Value · Week 13
Weigh each outcome by how likely it is and add them up; a small chance of a huge loss can outweigh a likely small gain.
How Much Should This Move Me? · Week 13
A fact counts as evidence by how much more expected it is if the claim is true than if it is false.
The Availability Heuristic · Week 26
Vivid stories are not counts; ask how many cases and out of how many.
Base Rates · Week 26
Before the story arrives, ask how common the thing is.
Valid Is Not the Same as True · Week 29
A valid argument guarantees its conclusion only when its premises are true, so check the form and the facts.
Bayes in Plain Words · Week 35
Start with how likely a claim was, then shift by how well the new evidence fits it.

Skepticism · 29 lessons

Bias, extraordinary claims and the patience to ask what would prove you wrong.

Confirmation Bias · Week 4
We notice what fits our beliefs, so record cases before judging them.
One Story Is Not a Rate · Week 4
One story shows that a thing can happen, not how often it does.
Correlation and Causation · Week 4
Two things moving together is a clue, not a cause.
The Burden of Proof · Week 4
Whoever makes a claim owes the reasons for it.
The Dunning–Kruger Effect · Week 4
Early confidence is a poor guide, so check it against a scored result.
The Baloney Detection Kit · Week 7
Extraordinary claims need evidence that could fail and that others can check.
Motive Is Not a Disproof · Week 7
A motive is a reason to check the evidence, not a way to skip it.
What a Source Owes You · Week 14
A good source lets you trace the claim back to a record.
Where Did This Come From? · Week 14
Before you believe or share, trace it: who made it, when, and what else says so.
What Would Prove It False · Week 14
A claim that can explain every outcome explains none.
Extraordinary Claims · Week 14
The stranger the claim, the stronger the evidence it needs.
Survivors Only · Week 14
A group filtered by success shows you its winners; ask who is missing from the picture.
Cherry-Picking · Week 14
Picking only the facts that fit a claim can make any claim look true.
Rough Numbers · Week 14
Break a big unknown into small guesses, and multiply to get an answer that is close enough to use.
Changing Your Mind Well · Week 18
Name in advance what would change your mind, and when it happens, say so plainly.
How Big a Sample? · Week 26
Small samples produce striking results by luck, so ask how many before you believe it.
Relative and Absolute Risk · Week 26
Ask for both numbers: how much a risk changed, and how many people it touches.
Misleading Charts · Week 26
Check the axis, the start date and the scale before you trust how steep a chart looks.
What “Significant” Means · Week 26
“Statistically significant” means unlikely to be chance alone, not large or important.
Headline Versus Study · Week 26
A finding can grow and change on its way from the paper to the headline, so check the source.
Framing · Week 30
The same facts can lead to different choices depending on how they are described.
Anchors · Week 30
The first number you hear pulls your estimates toward it, even when it is arbitrary.
How Sure Are You? · Week 30
Put a number on your confidence, then check later whether your sure answers were right as often as you said.
Painting the Target · Week 35
Drawing the target after the shots are fired makes a scatter look like skill.
Two Groups, One Trend · Week 35
A trend in the combined data can flip when you split the data into groups.
Once Is Not Enough · Week 35
A finding earns trust when different people can repeat it and get the same result.
Regression to the Mean · Week 35
After an extreme result, the next one tends to be closer to average, whatever you did in between.
The Linda Problem · Week 35
A detailed story can feel likelier than a plain one, yet each added detail makes it less likely.
Blind and Fair · Week 35
A fair test hides who got the real treatment, since expectations can change results.

The Modern Sage · 10 lessons

Where character, logic and inquiry have to work in the same hour.

The Experience Machine · Week 8
We want to do things, not only to feel as though we did.
The Modern Sage · Week 9
On a hard day, run three checks: what is mine, what is the claim, what is the evidence.
Disagreeing Well · Week 18
Restate their view until they would sign it, then give your reason and say what would change your mind.
Map an Argument · Week 30
To judge an argument, write down the conclusion, the premises and the gap between them.
Write a Short Argument · Week 30
State your claim, give two reasons, meet one objection, and stop.
Three Lenses on One Dilemma · Week 30
Look at a hard choice through virtue, duty and results, and see what each one shows.
A Week of Practice · Week 52
Pick one small habit from the course for seven days, and record what you notice each evening.
Teach It Back · Week 52
If you cannot explain an idea in plain words, you have found what to study next.
A Personal Creed · Week 52
Write a few sentences on what you hold and why, and revise them when life tests them.
The Summit Practice · Finale
One belief, one sentence, one act that is yours, one way it could fail, then stop.

Beauty and art · 9 lessons

What we mean by beautiful, why stories move us and whether anything can be called art.

Taste and Disagreement · Week 36
Taste is not arbitrary: better judges notice more, and their agreement is a fair guide.
Liking Without Wanting · Week 36
Delight in beauty is a pleasure that does not ask to own, use or eat the thing.
Beauty in What Passes · Week 36
What is fleeting or worn can feel more beautiful because it will not last.
Why Stories Move Us · Week 36
A story lets us feel strong things safely, and some of that feeling leaves us clearer.
In Praise of Shadows · Week 45
Tanizaki praised the beauty of shadow and dim light, which bright modern rooms had driven away.
What Makes It Art? · Week 51
No single feature marks everything we call art, so ask what a claim of “art” is doing.
Depth Beyond Words · Week 51
Yugen is beauty felt as depth: what is suggested moves us more than what is shown in full.
The Sublime · Week 51
The sublime is the thrill of something vast or powerful, felt from safety, which beauty’s calm pleasure does not capture.
The Perfect Fake · Week 51
If a forgery looks exactly like a masterpiece, why does finding out it is fake change how we value it?

Philosophy in practice · 17 lessons

Animals, shared resources, the future, climate, machines, privacy, consent and care, tested with the habits you already have.

The Trolley Problem · Week 29
When two cases with the same numbers pull your judgment apart, look for the difference that explains both.
Who Counts? · Week 31
Ask what feature makes a being matter, then check whether it marks the line you have been drawing.
The Common Pasture · Week 31
What is sensible for each user can ruin a shared resource, so groups need rules they can all accept.
People Who Do Not Yet Exist · Week 31
Our choices shape who will live, yet we can still owe them a decent world.
Who Pays for the Warming? · Week 31
Fair sharing of a shared problem asks who caused it, who can pay, and who is hurt most.
Think Like a Mountain · Week 31
Leopold’s land ethic widened the moral community to include soils, waters, plants and animals: the land as a whole.
Who Answers for the Machine? · Week 38
When a system decides, someone must still be able to explain the decision and correct it.
The Imitation Game · Week 38
Turing replaced “Can machines think?” with a test: can a machine’s conversation be told apart from a person’s?
What Would We Owe a Machine? · Week 38
If a machine could feel, it might deserve moral concern. The hard part is telling whether it does, and erring well.
Nothing to Hide? · Week 38
Privacy protects freedom to think and act without being watched, not just the ability to keep secrets.
Consent That Means Something · Week 39
A yes counts only if the person understood, chose freely and was able to decide.
When Help Becomes Control · Week 39
Overriding someone’s choice for their own good needs a strong reason and a test they could accept.
The Violinist · Week 39
Thomson’s violinist case asks whether a right to life includes a right to use another person’s body to stay alive.
A Good Death · Week 39
Is there a moral difference between letting a dying patient die and helping them die? Rachels questioned the line.
When Is War Just? · Week 39
Just war theory asks when going to war can be right and how it must be fought; pacifists reject war altogether.
The Prisoner’s Dilemma · Week 39
The prisoner’s dilemma shows how two people acting sensibly alone can both end up worse off, and how trust can fix it.
The Last Person on Earth · Week 42
Routley asked if the last person alive would do wrong by destroying a forest, testing nature’s value beyond use.

Women who reset ethics · 9 lessons

Four twentieth-century thinkers who asked what an act is, what a good life needs and how fairly we see one another.

The Kestrel · Week 18
Attending to something outside yourself, like a bird or a task, can quiet your own worries.
Attention Is Rare · Week 18
To ask a suffering person what they are going through, and then listen, is a rare and real gift.
Living With Grief · Week 18
Grief is less a problem to fix than love continuing after loss; the task is to give it a place.
Why Are You Doing That? · Week 32
An act is intentional when “why?” has an answer, and one act can have several descriptions.
The Good of a Plant · Week 32
We can call living things good or bad by what their kind needs, and humans need virtues.
Look Again · Week 32
Much of morality is how fairly you see a person before you decide what to do.
Reasons for Love · Week 43
Do we love people for their qualities, or do we come to value them because we love them? Plato and Frankfurt differ.
What Emotions Know · Week 43
Nussbaum argued that emotions are judgments about what matters to us, so they can be accurate, mistaken or educated.
Ought Without a Lawgiver · Week 43
Words can outlast the frame that gave them force, so ask what a heavy word still rests on.

Other roads · 13 lessons

Voices from India, Baghdad, Andalusia, Cairo, China, Europe, Ghana and Brazil that the other paths do not reach.

Two Roads to One Truth · Week 24
If reason and scripture seem to clash, one of the two readings may need another look.
The Feather and the Heart · Week 25
In ancient Egypt, Maat meant truth, justice and cosmic order, and a life was weighed against it.
The Eloquent Peasant · Week 25
A wronged farmer in an Egyptian tale argues nine times that officials owe Maat to the weak, and wins.
Whose Words Do We Think In? · Week 45
Check whether the ideas you inherit were chosen by you, and what your own language could say instead.
Know It and Do It · Week 48
Two Neo-Confucians disagreed on how to learn the good, and agreed it must show in what you do.
I and It · Week 48
We can meet a person as a whole presence, or use them as an object, and both happen daily.
The Face · Week 48
Another person’s face makes a claim on you before any theory does, and it cannot be fully summed up.
Double Consciousness · Week 48
Du Bois described double consciousness: seeing yourself through the eyes of a world that looks at you with contempt.
Banking and Dialogue · Week 48
Teaching treats learners as empty accounts, or as partners in asking about their own world.
Counting the Truth · Week 49
Du Bois answered racist myths with careful data, from door-to-door surveys to charts, and learned facts alone were not enough.
Fixed by a Glance · Week 49
Fanon described being fixed by a stranger’s glance into a racial image, and how colonial racism shapes even the self.
The Wretched of the Earth · Week 49
Fanon analyzed colonial rule and decolonization, and warned that independence can be captured by a new elite.
Democracy as a Way of Life · Week 49
Ambedkar argued that caste destroys fellow feeling, and that democracy must be a way of living together, not just voting.