Major Philosophers & Their Big Ideas

Teaching through a series of questions that expose contradictions in someone's beliefs and lead toward clearer definitions.

Recorded by Plato in the Apology.

The physical world is an imperfect copy of a higher realm of perfect, unchanging Forms (such as Justice or Beauty) that we know through reason.

Prisoners who see only shadows on a wall stand for people who mistake appearances for reality; the escaped prisoner who sees the sun is the philosopher who grasps the Forms.

A good life (eudaimonia, flourishing) comes from developing virtues of character, each a “golden mean” between two extremes (courage between cowardice and recklessness).

Focus only on what you can control (your judgments and actions) and accept what you can't. Key Stoics: Zeno, Epictetus, Seneca and Marcus Aurelius.

Not indulgence, but ataraxia (peace of mind) and freedom from pain, through simple living, friendship and freedom from fear of death.

Five arguments for God's existence, including the unmoved mover, the first cause and the argument from design. He combined Aristotle with Christian theology.

A ruler should do what keeps power and the state secure, even if it means being deceptive or cruel; it is safer to be feared than loved if you can't be both.

He could doubt everything except that he was doubting, and so thinking.

Mind-body (substance) dualism

Rationalism: knowledge comes mainly from reason (Descartes, Spinoza, Leibniz). Empiricism: knowledge comes mainly from sense experience (Locke, Berkeley, Hume).

“Solitary, poor, nasty, brutish, and short.” People give up freedom to a powerful sovereign (the Leviathan) in exchange for security.

The mind starts as a blank slate and is filled by experience. Locke also argued for natural rights to life, liberty and property.

We can't logically prove that the future will resemble the past, so generalizing from past experience is a habit, not a proof.

The is-ought problem (Hume's guillotine)

“To be is to be perceived”: physical objects exist only as ideas in minds (subjective idealism).

The collective will of the people aimed at the common good, which legitimate government should follow. The Social Contract opens: “Man is born free, and everywhere he is in chains.”

Act only on rules you could will to be universal laws, and treat people always as ends in themselves, never merely as means.

Deontology judges actions by duties and rules (Kant). Consequentialism judges actions by their outcomes (utilitarianism).

The right action produces the greatest happiness for the greatest number. Bentham counted all pleasures equally; Mill said intellectual pleasures are higher than bodily ones.

The harm principle

Often called the father of existentialism, he stressed individual choice, anxiety and the “leap of faith.”

Belief in God no longer grounds European values, leaving a crisis of meaning (nihilism) that people must overcome by creating their own values (the Übermensch).

There is no fixed human nature; we define ourselves through our choices.

“One is not born, but rather becomes, a woman,” from The Second Sex (1949).

The clash between our search for meaning and a silent universe. In The Myth of Sisyphus he says “one must imagine Sisyphus happy.”

Choose the rules of a just society without knowing what position you'll have in it. Rawls argued you'd pick equal liberties and help for the worst off.

Occam's razor

It is rational to believe in God: if God exists you gain infinitely, and if not you lose little.

Should you divert a runaway trolley to kill one person instead of five? Introduced by Philippa Foot (1967) to test the difference between doing and allowing harm.