In Metaphysics Book IX (chapter 8) Aristotle introduces a set of ideas central to his metaphysics as a whole: act and potency. Not only are these concepts important for Aristotle’s system, but they have also had a lasting influence on philosophy, and for pour purposes, cosmology; for, they advance upon the static (ideal) universe of Platonic thought and allow for real change in the cosmos.
Aristotle’s act is better understood as a noun rather than a verb, as ‘actuality’. Though the “word ‘actuality’ is derived from ‘action’”, it points to a “complete reality”1 and actualized thing. So when we speak of ‘act’ it is as the already actualized. Potency then is the capacity of a thing to become fully realized, fully actualized.
Upon first reflection, it appears as if potency is prior to actuality. Is not a tree first seed and a seed a potential tree? Aristotle however is careful to point out that both in the observable universe as well as in theory it is truly the other way around: “Actuality is prior to potency...” in both “formula and in substantiality.”2 Theoretically speaking, something cannot come from nothing, therefore “the actually existing is always produced by an actually existing thing.”3 A seed may potentially be a tree, but it itself comes from an already existing tree. As the historian of philosophy, Fredrick Copleston summarizes the point, “A natural object is in potency in regard to the full realization of its form, e.g. an acorn or a small tree in regard to its full development…”4 Theoretically and in the realm of experiential things, act is prior to potency.
Aristotle understands this movement unto actuality as related to concepts of privation and form. It is because the boy is not a man (privation) that he grows (moves); he is in a state of potentiality wherein he is becoming what he is (to be). Potentiality exists so that things may be actualized. This actualization, however, is a kind of determining process. “The actual is always produced from the potential, the potential is always reduced to act by the actual, that which is already in act, as man is produced by man.”5 Through a movement from privation, “potentiality is not simply the negation of actuality.”6 A seed is neither a boy nor a tree, yet it is potentially only the latter. Thus potency is a “power of self-actualization”7 according to a specific end. For “everything that comes to be moves towards a principle, i.e. an end (for that for the sake of which a thing is, is its principle, and the becoming is for the sake of the end).”8 This end is a realization of form. For “matter exists in a potential state, just because it may come to its form; and when it exists actually, then it is in its form.”9 Potentiality is a capacity for movement unto actualization of a form, that end is thus a formal cause.
At this point, it can be asked whether this is simply the Platonic theory of forms coming from the opposite direction. If act is the attainment of form, is not form prior (temporally as well as metaphysically) to things just as act is prior to potency? Aristotle would answer in the negative. For actualization may be the attainment of form, but form and act are not simply identical. An actual thing has reached its ‘intended’ form precisely in that is has become actualized and now shares that form “which is identical in a species.”10 Form lacks substantiality apart from actual things, yet the form of things (as informed substances) is the guiding principle of the movement to actualization. In other words, form is cause only because form is possessed by actualities for the sake of which potency exists. In this way, Aristotle need not conceive of an ideal realm of forms that is metaphysically prior to things for form is unsubstantial apart from actuality. Aristotelian formal abstraction holds.
This insistence on pre-existent actuality does however lead to some difficulties in the Aristotelian system. Something cannot come from nothing; thus Aristotle can posit the existence of a ‘prime mover’ from which all things came. Likewise, something cannot give what it does not have, thus Aristotle himself does not think of “prime mover” exclusively in the singular. “There is always a first mover, and the mover already exists actually”, yet he makes this affirmation in the context of “man” coming “from man, musicians by musicians”…etc.11 It is not so much that all things exist because of a prime mover, but that they exist as they are because of prime movers. This is not the timeless realm of ideal forms, but it is a universe that is continually becoming what it has been and will always be. Advancing upon his predecessors, he admits real change within the universe, but this change is not the ‘development’ of modern physics and evolutionary theory. The universe of Aristotle, therefore, is somewhere between the static ideal of Plato and the constructive chaos of later cosmology.
Aristotle, by appealing to the ideas of act and potency provides a compelling account for the real existence of change. Act is prior to potency and thus change is nothing less than the movement from the actual unto the actual.
Aristotle. Metaphysics, 9. 8.
Ibid., 9. 8.
Ibid.
Copleston, A History of Philosophy. Vol. I, Part II (New York: Image Books, 1962), 52-53.
Copleston, A History of Philosophy, 53-54.
Copleston, 53.
Ibid., 52.
Metaphysics, 9. 8.
Ibid.
Ibid.
Ibid.