The perfect action that has its end in itself is called by Aristotle: final act or final realization (entelechia). While the movement is the process that leads gradually to acting what was only potential, the 'entelechia' is the final term (telos) of the movement, its perfect conclusion. But as such, 'entelechia' is the accomplished realization and therefore the perfect form of what is becoming; it is the species and substance. Then, the act identifies itself in each case with the species and, when it is a perfect act or final realization, it coincides with the substance. This is the same reality under way and its principle. In front of it, the matter considered in itself, that is as pure material or raw material, absolutely deprived of actuality or form, is indeterminable and unknowable and is not substance.
Thus, entelechia is the term used by Aristotle in opposition to "power" to describe the reality that has reached the full level of its development; it is sometimes identified with the word 'act', but the two terms are different as the latter indicates the active realization of power, and the entelechia, instead, constitutes the perfect reached implementation by the substance. It is therefore not to be confused with the ‘endelechia’, term initially used by Aristotle and transmitted by Cicero, which is used to indicate the human soul understood as the ‘fifth nature’ (different from any other known to us), immortal, common to the gods and the heavens (divine beings).
The term entelechia was revived by Leibniz to indicate the Monad, as it has in it the perfect organic end of its development.
Now, in other words, the term ‘entelechia’ was coined by Aristotle to describe his particular philosophical conception of a reality that has registered in itself the ultimate goal toward which to evolve. It is in fact composed of en + telos, which in Greek means "inside" and "purpose", to mean a kind of "inner purpose".
Speaking of entelechia’ Aristotle opposed the Platonic theory of ideas, to assert how each entity develops starting from a final cause internal to it, and not by external ideal reasons as, instead, Plato argued by locating them in the hyperuranium sky. Entelechia is therefore the tension of an organism to realize itself according to its own laws, passing from potentiality to action.
It is known, in fact, as, according to Aristotle, ‘becoming’ can be considered fully explained when its four causes are identified: Material Cause, Formal Cause, Efficient Cause and the Final Cause. To designate the accomplishment of the purpose Aristotle used precisely the term entelechia that indicates the state of perfection of something that has reached its end.
Neo-platonists came in part to the Aristotelian concept that the shape of a body should also be immanent to it and not only Platonic transcendent, but found reductive the identification of the soul with entelechia, since the soul is something prior to the body and still independent of it.
A synthesis of the Aristotelian and neo-Platonic conception is in Tommaso Campanella, for whom nature is a complex of living realities, each animated and tending to its end, but then all unified and harmoniously directed toward a common goal by the same universal ‘Anima mundi’.
Leibniz also conciliated the Aristotelian entelechia with the Neo-Platonic vision, making it an essential property of the Monad, that is, of every "energy center", capable of developing independently towards their goal or destiny: each monad receives no impetus from the outside, but all together they form a single complex, regulated in the inside by a harmony preset by God, the supreme Monad. They are, in fact, equal to the coordinates of so many clocks, functioning on their own but synchronized with each other.
In the twentieth century the term ‘entelechia’ has been recalled by the philosopher and biologist Hans Driesch to designate the ‘vital energy’ which he considered immanent to embryos and responsible of their development, as opposed to mechanistic theories which they saw as a "machine."
In the light of the Aristotelian distinction between entelechia, as an action, a realized term of the action that contains no further progress, and ‘energeia’, that is the action understood as actualization of entelechia in the making, the misstep is configured as an impasse, a slip out of 'energeia’, out of the direct realization of ‘entelechia’. On the other hand, the concept of the raid of entelechia takes to a deviation whose subject is the ‘entelechia’ itself. The totality of the act is not only the purpose in the pure state, but a purpose enriched by all outings that can branch from it. The ‘real’ is the product of an ongoing process of experimentation, and "the rare flower of the event comes from a multiplicity of attempts and a renewal of evidence". A world without baroque deviations would be poor, schematic, unable to realize all the possibilities contained in the entelechia. The energeia has an ontological weight greater in a nature and in a story that integrate the missteps ".