A teleology is any philosophical account that holds that final causes exist in nature, meaning that — analogous to purposes found in human actions — nature inherently tends toward definite ends.
Teleology was explored by Plato and Aristotle, by Saint Anselm during the 11th century AD, in the late 18th century by Immanuel Kant as a regulative principle in his Critique of Judgment and by Carl Jung. It was fundamental to the speculative philosophy of Hegel.
A thing, process, or action is teleological when it is for the sake of an end, i.e., a telos or final cause. In general, it may be said that there are two types of final causes, which may be called intrinsic finality and extrinsic finality.
A thing or action has an extrinsic finality when it is for the sake of something external to itself. In a way, people exhibit extrinsic finality when they seek the happiness of a child. If the external thing had not existed that action would not display finality.
A thing or action has an intrinsic finality when it is for none other than its own sake. For example, one might try to be happy simply for the sake of being happy, and not for the sake of anything outside of that.
Since the Novum Organum of Francis Bacon, teleological explanations in science tend to be deliberately avoided because whether they are true or false is argued to be beyond the ability of human perception and understanding to judge. Some disciplines, in particular within evolutionary biology, continue to use language that appears teleological when they describe natural tendencies towards certain end conditions. While some argue that these arguments can be rephrased in non-teleological forms, others hold that teleological language is inexpungeable from descriptions in the life sciences.