Teleology (telos: end, purpose) is the supposition that there is design, purpose, directive principle, or finality in the works and processes of nature, and the philosophical study of that purpose.
Teleology stands in contrast to philosophical naturalism, and both ask questions separate from the questions of science. While reductionist science investigates natural laws and phenomena, philosophical naturalism and teleology investigate the existence or non-existence of an organizing principle behind those natural laws and phenonema. Philosophical naturalism asserts that there are no such principles. Teleology asserts that there are.
For example, the view of philosophical naturalism is that man sees because he has eyes. Teleology, on the other hand, holds both that man sees because he has eyes and has eyes so that he can see. As Aristotle wrote in support of teleology, "Nature adapts the organ to the function, and not the function to the organ" (). Lucretius replied in support of philosophical naturalism: "Nothing in the body is made in order that we may use it. What happens to exist is the cause of its use." ()
Teleology also has a technology-oriented history. The study of "teleological mechanisms" in machinery (i.e. machines with corrective feedback) dates back at least to the late 1700s when James Watt's steam engine was equipped with a governor. The 1943 paper "Behavior, Purpose and Teleology" by Arturo Rosenblueth, Norbert Wiener, and Julian Bigelow provides a conceptual framework. One of these authors, the famous mathematician Norbert Wiener, coined the term 'cybernetics' to denote the study of "teleological mechanisms," which was popularized through his book Cybernetics, or control and communication in the animal and machine (1948). Cybernetics is the study of the communication and control of regulatory feedback, both in living beings and machines, and in combinations of the two. Since that time the term "teleologic" in particular has been frequently used in the scientific literature to capture the sense of purposeful, iterative, goal-directed behavior in biological and technological control systems.
Teleology in Biology
Contemporary accounts of teleology within biology are heavily influenced by Larry Wright's "etiological" account of teleology. Wright's attempt was to provide a definition of function that could be applied to natural phenomena as well as human artifacts - that is, human constructions such as a hammer.
Most contemporary accounts of teleology follow in the steps of Wright's etiological account (Millikan for instance), however there is disagreement over its use. Some, such as Godfrey-Smith and Mayr, object to any sort of etiological theory of teleology that attempts to explain both natural phenomena as well as human artifacts. Their accounts therefore are therefore naturalistic accounts of teleology.