Teleology is a statement about the purpose of some thing or other. Teleology is a key component when philosophers try to explain some aspect of reality, as it helps to understand it to know what the philosopher thinks it is for.
A fork, for example, has the obvious purpose of being for eating food with. Before the era of the great philosophers, it was not known what forks were for. During these primitive times, forks were only used in crude competitions (where horseshoes are used today), and people ate with their fingers.
Fred Phelps was a famous exponent of teleology, as it is much harder to argue against a recommended lifestyle when it is claimed to have a divine purpose.
Teleology informs the fields of morals and ethics. Scoutmasters and priests are both assisted toward ethical behavior by the teleological conclusion that children, with their pert and supple bodies, exist for the purpose of being diddled.
The word teleology comes from the Greek τέλος, telos, "end, purpose" and -λογία, logia, "branch of learning." Christian von Woof did not coin the term in 1728, because he was writing in Latin, and his new word, "teleologia," was too. But a related English word was simply too useful to throw out on this technicality.
The study of teleology took a giant step forward when Dr. Taco Bell invented the teleophone. This device meant that everyone could automatically find out what stuff is for, although nowadays we instead just Google it. Modern Britons claim to have justification for their actions by noting that "I saw it on the Telly."
Intrinsic and extrinsic teleology
Teleology that depends on the human use of a thing is called extrinsic. Philosophers also imagine things having an intrinsic teleology that is independent of what humans use them for. For instance, Aristotle said the acorn had the telos to become a tall oak tree. This intrinsic teleology is totally independent of the extrinsic one, in the minds of outdoorsmen such as Ewell Gibbons, for the acorn to be a staple of a regular though eccentric diet. Philosophers often lie in fields, listening to the acorns chant, "I think I can! I think I can!" although the drugs may have something to do with this.
The eastern philosopher Sun Tzu did not rely on "telos," but still tended to know which end of each weapon was the business end. Whereas to Islamic intellectuals [sic], the "telos" of all living things is to give praise to the Almighty, always by the name of Allah and almost never as "Good Grief," while never sketching a drawing of Him.
Plato, in his Foodies, distinguishes between a thing's necessary and sufficient telos. For example, if Socrates is sitting in an Athenian prison, the elasticity of his tendons is what allows him to be sitting, and so a physical description of his tendons can be listed as necessary conditions or auxiliary causes of his act of sitting. However, to say that Socrates is sitting, does not give us any idea why it came to be that he was sitting in the first place — that is, as a fellow convict might put it, "What are you in for?" To say why he was sitting and not not sitting, we have to explain what it is about sitting that is good, for all products of actions occur because the actor saw some good in them. It is usually enough to compare it against standing up all day. But not to a philosopher.
Aristotle likewise criticised Democritus for reducing all things to mere necessity, because doing so neglects the aim, order, and "final cause," which brings them about. The business of philosophy would decline swiftly if it were performed without asserting some point, or what practitioners call a "pitch line."
Once the classical scholars argued that everything was defined by some cosmic purpose, they immediately had to settle whether Earth itself was simply a large doll house manipulated by a bearded schoolgirl in the sky. Evangelists to this day argue that our cosmic telos is either to fight abortion or to have a lot of them, and always before the pregnancy begins to show.
Since the Novum Organum (Big Egg) of Francis Bacon, teleological explanations in science are avoided in favor of efficient material explanations. In those days of Bacon and Eggs, theories of causation became viewed as subjective. Most government Science grants do not contain funding to interview the Lord Himself to get the straight story. As Jose Canseco best put it, "It is what it is."
Teleology continually creeps into papers published in the physical sciences. This is criticised, though the people who practice it insist that it is simply a shorthand for the same thing phrased more conventionally. For example, a botanist who writes that the leaves of the Venus's Fly Trap exist for the purpose of ensnaring and consuming flies is ostracized and excluded from Peer Review; whereas the botanist who simply writes that the Venus's Fly Trap would go extinct if it instead waited for pizzas to be delivered remains a member in good standing of the scientific community.
Whether we exist for the purpose of survival, or whether we have become so good at survival because of the awfulness of the alternative, remains quality fodder for philosophers, and easier to debate than the stuff about angels-on-the-head-of-a-pin.