In the usage of Aristotle, entelechy (Gr. 'εντελϡεξεια, from 'εν τϡελει 'εξειν, to have something in fulfillment; to be complete) is an analogical word. It has two most basic uses: (1) to designate the state of achievement or fulfillment that is like knowledge acquired and possessed (this is its first imposition); and (2) to designate the state of fulfillment, presupposing what is like knowledge possessed, that is like the actual entertaining or considering of knowledge possessed. For example, having acquired, and thus in possession of, knowledge of a geometric proof, one has fulfilled to some extent his natural capacity for learning. But he does not spend the rest of his life thinking through the steps of the proof. Actually thinking through the steps of the proof represents another and distinct sort of fulfillment. Before one has learned the proof, he is capable of learning it. Having learned the proof, he is capable of thinking through its steps. Corresponding to each of these two states of capability is a state of fulfillment, an entelechy. Knowledge possessed is simultaneously, but in different relations, both entelechy and capability. Actually thinking through the steps is impossible without knowledge possessed. This is why what is like knowledge possessed has been called first entelechy—first in an ontological sense, that without which something else cannot be or occur. This is also why what is like actually thinking through the steps has been called second entelechy. (See Aristotle, Anim. 412a 10–12; 417a 21–417b 2.)
Aristotle's purpose in distinguishing these two senses of entelechy was to make clear the sense of the first of his two common definitions of the soul: the first entelechy (actuality or act is a usual rendering) of a natural body having life potentially in it, i.e., of a natural organized body. The natural organized body of a living thing is related to its soul in the way in which man, taken as a knower, is related to knowledge possessed. The living thing, i.e., the compound of natural organized body and soul, is related to its vital operations (e.g., nourishing, sensing) in the way in which the knowing man, i.e., the compound of human knower and knowledge possessed, is related to actually thinking through the steps. Thus, the natural organized body of a living thing has a twofold entelechy: (1) soul, and (2) vital operations. Soul, being the ontologically prior, i.e., accounting for the ontological status of a living thing as living thing (this is why it is said to be a substantial form), and being that which vital operations presuppose and upon which they depend, is said to be the first entelechy of such a body; a vital operation, a second entelechy.
The suggestion of G. W. leibniz that his monads may be called entelechies, since they have in themselves a certain perfection consisting in their nonconscious perceptions, represents a usage differing from Aristotle's in that it designates something that is simple and also a substance. Aristotle's designates something simple, indeed; but something related to a substance, and not a substance itself.
Hans Driesch develops a notion of entelechy in the course of a lengthy argument against biological mechanism and for biological vitalism. Entelechy is an elemental agent in nature, over and above physical and chemical agents and configurations thereof, that in the realm of living things accounts for all the order in morphogenesis, and uses the genes as its means to account for inheritance. More generally, it directs life activities and everything material that is used in their performance. It is not a kind of energy, nor is it something quantitative, nor divisible, nor a force; it is not space, but has manifestations in space; it is substance, but only in the sense of what accounts for the ordered wholeness of a living thing; it is a cause, but only in an actual state, as actually accounting for wholeness (since it can also appear in a potential state). Driesch's concept of entelechy is clearly not incompatible with that of Aristotle; but whereas Aristotle's use of entelechy apropos of soul focuses on soul's function as the formal cause constituting a thing a living being, Driesch's can be said to focus on soul's function as efficient or agent cause in relation to the biological development and behavior of the living thing.
See Also: soul, human.
Bibliography: g. giannini, Enciclopedia filosofica, 4 v. (Venice-Rome 1957) 1:1919–25. g. w. leibniz, The Monadology, in his Discourse on Metaphysics, Correspondence with Arnauld, and the Monadology, tr. g. r. montgomery (La Salle, Ill. 1962). h. driesch, The Science and Philosophy of the Organism (2d ed. London 1929).
"Entelechy." New Catholic Encyclopedia. . Encyclopedia.com. (September 18, 2018). http://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/entelechy
"Entelechy." New Catholic Encyclopedia. . Retrieved September 18, 2018 from Encyclopedia.com: http://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/entelechy