telos ancient Greek term meaning ‘end’ or ‘purpose’. Telos is a key concept not only in Greek ethics but also in Greek science. The purpose of a human being is a good life, and human activities are evaluated according to whether they lead to or manifest this telos. Plants, animals, and even inanimate objects were also thought to have a telos through which their activities and relations could be understood and evaluated. Though a telos could be something that transcends human activities and sensible things, as Plato thought, it need not be anything apart from nature. Aristotle, e.g., identified the telos of a sensible thing with its immanent form. It follows that the purpose of the thing is simply to be what it is and that, in general, a thing pursues its purpose when it endeavors to preserve itself. Aristotle’s view shows that ‘purpose in nature’ need not mean a higher purpose beyond nature. Yet, his immanent purpose does not exclude ‘higher’ purposes, and Aristotelian teleology was pressed into service by medieval thinkers as a framework for understanding God’s agency through nature. Thinkers in the modern period argued against the prominent role accorded to telos by ancient and medieval thinkers, and they replaced it with analyses in terms of mechanism and law. E.C.H.