What is philosophy?

The word philosophy comes from Greek words meaning love of wisdom. At its simplest, philosophy is the careful, reasoned investigation of fundamental questions: what exists, what we can know, how we should live and what makes an argument good.

Philosophy differs from science in its methods rather than its curiosity. Science tests claims through observation and experiment. Philosophy mostly works through argument, analysis of concepts and thought experiments, often tackling questions that experiments alone cannot settle, such as what makes an action right.

• Metaphysics: the nature of reality, including time, causation, identity and whether minds are physical.
• Epistemology: the nature and limits of knowledge, and what justifies believing something.
• Ethics: how we ought to act and what makes a life good.
• Logic: the principles of valid reasoning.
• Political philosophy: justice, rights, authority and the legitimacy of government.
• Aesthetics: the nature of beauty and art.

Philosophy developed in several places independently. In ancient Greece, thinkers from Thales in the sixth century BCE onward sought natural explanations for the world instead of relying on myths. Socrates, Plato and Aristotle shaped much of Western thought.

In roughly the same era, Confucius and Laozi founded traditions that shaped Chinese thought, while in India the Upanishads and later schools, including Buddhist and Nyaya philosophy, explored the self, knowledge and logic in depth. Islamic philosophers later preserved and developed Greek ideas, and African, Mesoamerican and many other traditions developed their own systems of thought.

Philosophers often use imagined scenarios to test ideas. In the Ship of Theseus, a ship has every plank replaced over time. Is it still the same ship? The puzzle raises questions about identity that apply to people too, since the cells in our bodies are constantly replaced.

In the trolley problem, a runaway trolley will kill five people unless you divert it onto a track where it will kill one. Most people say they would pull the lever, but far fewer would push a person into its path to achieve the same result. Explaining that difference has proved surprisingly hard and reveals tensions between different moral principles.

A philosophical argument sets out premises and draws a conclusion. Critics then ask two questions: are the premises true, and does the conclusion actually follow from them? Philosophers look for hidden assumptions, counterexamples and consequences their opponents might not accept.

This habit of charitable but rigorous criticism is one of philosophy's lasting contributions. It underlies academic debate, legal reasoning and the scientific practice of trying to disprove one's own hypotheses.

Many sciences began as branches of philosophy. Physics was once called natural philosophy, and psychology, economics and linguistics all separated from philosophy as their methods matured.

Philosophical questions remain alive in modern debates: whether machines could ever be conscious, how to weigh the interests of future generations, what free speech should protect, and how to decide who counts as a person in medicine and law. Studying philosophy trains people to think clearly about such questions and to recognise weak arguments.