Aristotle (384 to 322 BCE) was born in Stagira in northern Greece, the son of a court doctor. At about seventeen he joined Plato's Academy and stayed some twenty years. Later he tutored the young Alexander of Macedon and, around 335 BCE, founded his own school in Athens, the Lyceum. His followers were called Peripatetics, perhaps from the covered walkway where they talked. Aristotle wrote on almost everything: logic, physics, biology, ethics, politics, poetry and rhetoric. What survives is mostly lecture notes, which explains their compressed style.

Logic

Aristotle was the first to study logic as a subject of its own. His central tool is the syllogism, an argument in which a conclusion follows necessarily from two premises. The classic example: All humans are mortal; all Greeks are humans; therefore all Greeks are mortal. Aristotle classified which forms of syllogism are valid. His logical works were later collected as the Organon, meaning “instrument,” and they dominated logic for about two thousand years.

Empirical method and the four causes

Where Plato looked upward to the Forms, Aristotle looked closely at the world. He insisted that knowledge begins with the senses and that forms exist in things, not apart from them. He dissected animals, studied marine life on the island of Lesbos, and classified hundreds of species. He also made errors, such as the belief that heavier objects fall faster.

To understand anything, Aristotle said, we must know its four causes (better translated as four kinds of explanation):

• Material: what it is made of (the bronze of a statue).
• Formal: its shape or structure (the design of the statue).
• Efficient: what brought it about (the sculptor).
• Final: its purpose or end, in Greek telos (to honor a god).

The final cause was central for Aristotle. He believed that natural things, not only artifacts, have ends: an acorn grows toward being an oak, and the eye exists for seeing. This purposive view of nature, called teleology, was later rejected by modern physics, though biologists still find talk of function useful.

Virtue and the mean

In the Nicomachean Ethics, Aristotle asks what the highest human good is. His answer is eudaimonia, often translated happiness but better rendered flourishing or living well. It is not a feeling but an activity: living in accordance with virtue over a complete life. Since humans are rational animals, our flourishing involves using reason well.

Virtues of character, he argued, are developed by habit, the way one becomes a builder by building or a harp player by playing. We become brave by doing brave acts. Each virtue is a mean between two vices, one of excess and one of deficiency. Courage lies between rashness and cowardice; generosity between wastefulness and stinginess. The mean is not a mathematical midpoint; it is “relative to us” and depends on the situation. Finding it requires practical wisdom (phronesis), the ability to see what a situation calls for.

Aristotle also wrote movingly about friendship, distinguishing friendships of usefulness, of pleasure and of virtue, and counting the last as the best and most lasting.

Critics have asked whether the doctrine of the mean gives clear guidance, since it seems to tell us only to do the right amount at the right time. Others note that Aristotle's flourishing life assumed leisure, wealth and citizenship available to few. Even so, his approach, now called virtue ethics, has been revived by modern philosophers who find it richer than rules alone.

Worked example: four causes and a mean

Let us apply Aristotle's tools to an ordinary object and an ordinary choice.

The object: a wooden chair.

• Material cause: the oak it is made from.
• Formal cause: its design, four legs, a seat and a back arranged in a certain way.
• Efficient cause: the carpenter working with tools.
• Final cause: to be sat on comfortably.

Notice that the final cause explains the others. The carpenter chose oak because it is strong enough to hold a person, and the design follows from the purpose of sitting. For Aristotle, asking “what is it for?” is often the most illuminating question.

The choice: telling a friend a hard truth. Dana's friend has written a business plan with a serious flaw and asks for an opinion. One vice would be flattery: praising the plan to avoid discomfort. The opposite vice would be harshness: listing every fault bluntly, perhaps in front of others. The virtue, a kind of honest friendliness, lies between them. But where exactly? Aristotle would say it depends on the friend, the stakes and the moment. If the friend is about to invest life savings, Dana should be clear and direct. If it is an early draft, gentle questions may be better.

No rule settles this. Dana needs practical wisdom, built up through experience, to see what the situation calls for. And she becomes the kind of person who can do this well by practicing it, which is Aristotle's point about habit.