What is philosophy? The big questions, made simple

Philosophy is the careful, reasoned study of basic questions that can't be settled by measurement or experiment alone: what exists, what we can know, how we should live, and what makes a piece of reasoning good. As a practice, philosophy works by argument: stating a view clearly, giving reasons for it, and testing it against objections and counterexamples. The word comes from the Greek for "love of wisdom".

In short

• Philosophy asks questions that evidence alone can't answer, such as what knowledge is or what makes an act right, and answers them with arguments.
• Its main branches are metaphysics (what exists), epistemology (what we can know), ethics (how to live) and logic (what follows from what).
• Reading philosophy well means finding the conclusion, listing the reasons, and asking whether the reasons are true and actually lead there.

What questions does philosophy ask?

Philosophy covers any subject where the hard part is the concepts, not the data. A scientist can measure how the brain responds to pain; whether the pain is something over and above that brain activity is a philosophical question. A court can decide what the law says; whether the law is just is a philosophical one.

The main branches, with one famous question each:

Branch	What it studies	A famous question
Metaphysics	what exists and what it is like	If every plank of a ship is replaced, is it the same ship?
Epistemology	knowledge, evidence and belief	What is the difference between knowing something and just being right?
Ethics	right and wrong, and how to live	Is it right to harm one person to save five?
Logic	what makes reasoning valid	When does a conclusion follow from its premises?
Political philosophy	power, justice and the state	What, if anything, gives a government the right to rule?
Philosophy of mind	minds, thought and consciousness	Could a machine ever feel anything?

The first question in that table is the puzzle of the Ship of Theseus, about how a thing stays itself through change. Philosophers often work with thought experiments like it: imagined cases, built to isolate one idea, that test a principle the way a laboratory test isolates one variable.

How is philosophy different from science?

Science asks what is the case and tests answers against observation; philosophy asks what our concepts mean, what follows from them and what would justify a belief, and tests answers against argument. The two overlap more than this suggests. Physics was called natural philosophy until the 1800s: Isaac Newton's great work of 1687 is titled Mathematical Principles of Natural Philosophy. Psychology, economics and linguistics each grew out of philosophy, and philosophers still work on what science assumes, such as what counts as a good explanation. One tool from that work is Occam's razor, the rule of preferring explanations with fewer assumptions.

Philosophy also differs from opinion. Saying "I think lying is always wrong" is an opinion. Philosophy begins when you give a reason ("because it treats the other person as a tool") and then face the objection ("what about lying to a murderer asking where your friend is hiding?").

How do you read a philosophical argument?

An argument is a set of reasons, called premises, offered for a conclusion. Two questions decide whether it works, as the Internet Encyclopedia of Philosophy puts it. Is it valid: if the premises were true, would the conclusion have to be true? And is it sound: is it valid, and are the premises actually true? A valid argument can have a false conclusion if a premise is false; a sound one cannot.

Worked example: a short paper that changed a definition

Many philosophers, tracing the idea back to Plato, held that knowledge is justified true belief. You know something if you believe it, it is true, and you have good reason to believe it. In 1963 Edmund Gettier published a two-and-a-half-page paper attacking that view. Here is how to take it apart.

1. Find the target. The claim under attack: any justified true belief is knowledge.
2. Find the case. Smith has been told by the company's president that Jones will get a job they both applied for, and he has counted ten coins in Jones's pocket. He concludes: "The man who will get the job has ten coins in his pocket." In fact Smith gets the job, and by chance Smith also has ten coins in his pocket.
3. Check each condition. Smith believes the sentence. It is true. He had good reasons for it. So it is a justified true belief.
4. Test it against intuition. Did Smith know it? Almost everyone says no: he was right by luck.
5. Lay out the logic. If justified true belief were always knowledge, Smith would know. Smith doesn't know. So justified true belief is not always knowledge. The argument is valid, and the only way out is to deny a premise, for example by saying Smith does know.

Most philosophers accepted the conclusion, and epistemology has spent the decades since trying to say what the missing ingredient is. One counterexample was enough because the claim was a definition: it said all cases, so one case that breaks it is decisive.

A checklist for any argument, in a book, an op-ed or a conversation:

• What is the conclusion? Often it's stated last, after "so" or "therefore".
• What are the reasons? List them as numbered premises.
• Is anything unstated? Most arguments rely on a hidden premise. Write it down.
• Is it valid? If every premise were true, must the conclusion be?
• Are the premises true? Look for a counterexample to each.
• Is this the strongest version? Restate it in the form its supporters would accept before criticizing it.

These are the same skills taught as critical thinking, applied to the hardest questions.

Where did philosophy begin?

It began in several places at once. In Greece, from the 6th century BCE, thinkers asked what the world is made of, and Socrates, who wrote nothing and was executed in Athens in 399 BCE, turned philosophy toward how to live, saying at his trial that "the unexamined life is not worth living." His student Plato wrote dialogues such as the Republic, which holds the allegory of the cave.

In China, Confucius, traditionally dated 551 to 479 BCE, taught that a good society rests on cultivated character and right relationships, and Daoist thinkers questioned fixed categories altogether. In India, schools debated logic, knowledge and the self, and the Buddhist philosopher Nagarjuna, around the 2nd century CE, argued that nothing exists independently. Medieval philosophers in the Islamic world, such as Ibn Sina (Avicenna) and Ibn Rushd (Averroes), carried Greek philosophy forward and shaped European thought. Each tradition has its own questions, not only versions of the Greek ones.

What use is philosophy?

It trains a particular skill: holding an idea still long enough to see what it commits you to. Many ideas people live by are philosophical, whether they know it or not. Stoicism began as a philosophy of how to bear what you can't control; nihilism asks what is left if nothing has built-in meaning. Philosophy also teaches calibrated doubt, knowing what you don't know, which connects to research on the Dunning-Kruger effect.

Still argued

Philosophers argue about whether their field makes progress. David Chalmers, writing in 2015, used a 2009 survey of professional philosophers at 99 leading departments, mostly in the English-speaking analytic tradition, to show how little agreement there is. On free will, 59% accepted or leaned toward compatibilism, the view that free will fits with a world governed by physical laws, 14% toward libertarianism and 12% toward no free will. On ethics, 26% favored deontology, 24% consequentialism and 18% virtue ethics. Chalmers concludes there is real progress, but less than in science. Others reply that philosophy's progress is in clarifying questions, and that when a question becomes answerable it leaves to found a new science.

Check yourself

• Without looking back: what makes a question philosophical rather than scientific? Give an example of each about the same subject.
• What is the difference between a valid argument and a sound one?
• Retell Gettier's coin case and explain why one example was enough to refute a definition.

Sources

• Validity and soundness — Internet Encyclopedia of Philosophy
• Gettier problems — Internet Encyclopedia of Philosophy
• Socrates — Stanford Encyclopedia of Philosophy
• Confucius — Stanford Encyclopedia of Philosophy
• Why isn't there more progress in philosophy? — David J. Chalmers, Philosophy, 2015