John Sellars on Aristotle, the Four Causes, and Nicomachean Ethics

Speakers: John Sellars (guest), Alex O'Connor (host)

A guided tour of Aristotle, taken in the order Sellars thinks best: metaphysics first, ethics last. Sellars rates Aristotle not because he was right about everything but because of how his mind works — the refusal to let a question stay simple, the habit of stating an answer and then refining it again and again. The through-line is that Aristotle is, above all, a biologist: his account of being, cause, soul, and the good life all grows out of trying to understand living organisms.

Key ideas

1. Aristotle answers the paradox of change with actuality and potentiality. The early Greek thinker Parmenides argued that things simply are — nothing can come from nothing, so change is impossible. Aristotle replies that an acorn is two things at once: actually an acorn, and potentially an oak tree. Potentiality — a real capacity to become something, not mere nothing — is part of what a thing is; the acorn is not potentially a chicken. You cannot understand a thing without knowing what it can become.

2. Form is the organisation of matter, not a separate eternal object (hylomorphism). Against his teacher Plato, who placed the true ‘forms’ in a changeless realm the physical world only imitates, Aristotle brings form down to earth. Hylomorphism — from hyle (matter) and morphe (form) — says a thing just is matter arranged in a structure. Destroy every chair and no ‘chairness’ is left over. Plato starts from the form and treats objects as its reflections; Aristotle flips it — objects come first, and forms are read off them.

3. To explain anything you need all four causes, above all its purpose. Aristotle’s four causes are better read as four explanations: what a thing is made of (material), its structure (formal), what brought it about (efficient), and what it is for (final, the telos). A table and a chair may share wood, legs, and a flat top; only their purpose tells them apart. Sellars insists this teleology — explanation by end or function — survives evolution: the heart is for pumping blood, and Darwin explains how such functions arose without a designer, rather than explaining them away.

4. The soul is the form of a living body — capacities, not a ghost. A corpse has all the right matter arranged the right way, yet it is dead; something is missing. Aristotle’s word is psyche, translated ‘soul’, but he means only what makes a thing alive: its capacities. Plants can grow and reproduce; animals add movement and perception; humans add thought. Soul here is not an immortal thing that departs at death — knock over a tower and its ‘soul’ (its form as a tower) is gone, not floated off.

5. The good life is fulfilling the human function — the exercise of reason. Aristotle’s ethics starts from function: just as a good instrument does well what it is for, a good human fulfils the specifically human function, which he identifies as reason. The good life — his term is usually translated ‘happiness’ — is then not a pleasant feeling but the condition of exercising that defining capacity well. Virtue is developed character, not a rulebook, and most virtues sit as a mean between two vices — courage between cowardice and recklessness — though not all (there is, Sellars notes, no moderate amount of adultery).

Context

Metaphysics grows from biology. Sellars’s organising claim is that Aristotle is first a natural scientist — a biologist bent on understanding organisms — and that his abstract doctrines are tools for that end. His chosen enemy is Democritus the atomist, an early ‘reductive materialist’ for whom everything is atoms in motion. Aristotle’s objection is that inert matter in motion is too thin to explain life: break an acorn into its components and you have said nothing about trees. Form, capacity, and purpose are needed to complete the picture.

Final causation and the evolution objection. The modern reader distrusts the idea that nature contains purposes, yet biology textbooks still say the heart exists to pump blood and leaves exist to photosynthesise. Sellars and O’Connor converge on a reconciliation: swap the loaded word ‘purpose’ for the neutral word ‘function’. An eye designed by an inventor and an eye shaped by natural selection both have a genuine function; evolution removes the built-in cosmic design, not the fact of function. As O’Connor puts it with a homely analogy, ask why a rocket is heading to the space station and the engineer answers with thrust and escape velocity, but the same person at the pub answers ‘because we want to do some science’ — both true, different kinds of explanation.

God as the unmoved mover. Aristotle did believe in God, but not the modern Christian creator. His universe is eternal and uncreated, so his God is no chronological first cause like a Big Bang. Rather there must be an unmoved mover to tie up our explanations and stop the chain of causes running back forever — an eternally existing source of all the motion and activity in the world. Sellars links this to Aristotle’s astronomy: eternal motion cannot run in a straight line, which has a start and an end, but only in a circle — and looking up, Aristotle saw the heavenly bodies wheeling round and round, seemingly there forever, and took them to be divine.

Logic as the algebra of argument. Aristotle invented formal logic. Before him, Plato’s Socrates argued well or badly by intuition; Aristotle wanted to formalise when a conclusion follows necessarily from its premises. His syllogism strips away content to expose structure — all A are B, all B are C, therefore all A are C — valid regardless of what you plug in, ‘like algebra, but for argumentation’. The point, partly, was to give people the tools to detect the sophist pulling the wool over their eyes.

Ethics as naturalistic, descriptive and normative. Because the human being has a function, ethics need not rest on divine command or free-floating ‘oughts’. A person who never governs their appetites or thinks through decisions is a bad human in the same plain sense that a wobbly table is a bad table — they fail to actualise their defining capacity. Yet Sellars grants a normative pull beyond bare description. The social virtues follow from a second Aristotelian definition of the human: not only rational animal but social animal, dependent from birth on others — the belief that we are self-sufficient individualists is, he says flatly, a lie. Virtue ethics therefore cultivates character traits fit for unique situations rather than blunt rules, and locates most virtues at the mean, with honest exceptions (there is no moderate amount of adultery).

See also

• John Sellars — the guest; historian of ancient philosophy at Royal Holloway.
• Alex O'Connor — the host of Within Reason.
• Aristotle — the subject; the philosopher whose metaphysics and ethics the episode surveys.
• Jonny Thomson on Epicurus, Hedonism, and the Good Life — sibling Within Reason episode on ancient ethics and the good life.