Act, Potency, and Energy

1 “Energy, from the Greek energeia (en, in; ergon, work), originally a technical term in Aristotelian philosophy denoting ‘actuality’ or ‘existence in actuality,’ means, in general, activity or power of action” (The Encyclopedia of Philosophy, ed. Paul Edwards [New York: Macmillan Publ. Co., 1967], s.v. “energy”). 2 For the meaning and translation of the term energeia and its relation to the term entelecheia, see the following: Rémi Brague, “Aristotle’s Definition of Motion and Its Ontological Implications,” trans. Pierre Adler and Laurent d’Ursel, Graduate Faculty 207 The Thomist 75 (2011): 207-43 ACT, POTENCY, AND ENERGY THOMAS MCLAUGHLIN St. John Vianney Theological Seminary Denver, Colorado E NERGY IS ARGUABLY the most encompassing and fundamental physical notion in modern science. Physicists speak of energy with respect to all four fundamental forces of nature: gravity, electromagnetism, and the strong and weak nuclear forces. Motion and heat have energy. Mass is a form of energy. More recently, astronomers have discovered dark energy, whose nature is largely unknown but which makes up seventy-four percent of the universe. The Law of the Conservation of Energy is one of the most important physical laws. The notion of energy is found not only in physics and astronomy but also in chemistry and in the earth and life sciences. Analogically, it is used in economics and other such disciplines, and it is, of course, enormously important in public policy. Etymologically, the word “energy” comes from Aristotle. Energeia, from en, meaning “in,” and ergon, meaning “work,” is a transliteration of a word invented by Aristotle and signifies a basic principle in his philosophy.1 In Thomas Aquinas’s Latin, this term is rendered as actus, operatio, or agere. The Greek and the Latin terms are commonly translated into English as “act,” “actuality,” or “activity.”2 The notions of work, kinetic energy, THOMAS MCLAUGHLIN 208 Philosophy Journal 13 (1990): 1-22; Joseph Owens, C.Ss.R., “Aristotle—Motion as Actuality of the Imperfect,” Paideia (1978): 120-32; George A. Blair, “The Meaning of ‘Energeia’ and ‘Entelecheia’ in Aristotle,” International Philosophical Quarterly 7 (1967): 101-17. 3 “As the phrase ‘Potential Energy,’ now so generally used by writers on physical subjects, was first proposed by myself in a paper ‘On the General Law of the Transformation of Energy,’ read before the Philosophical Society of Glasgow, on the 5th of January, 1853 . . .” (William Rankine, “On the Phrase ‘Potential Energy,’ and on the Definitions of Physical Quantities” [1867] in Miscellaneous Scientific Papers, ed. W. J. Millar [London: Charles Griffin and Co., 1881], 229). Rankine also asserts that the scientific meaning of “energy,” which was first introduced by Thomas Young in 1807, harmonizes “perfectly with the etymology of enevrgeia” (ibid., 230). 4 William Rankine, “On the History of Energetics,” The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science 28, fourth Series, no. 190 (London: Taylor and Francis, 1864), 404. 5 James Clerk Maxwell, Matter and Motion (1877), with notes and appendices by Sir Joseph Larmor (Mineola, N.Y.: Dover, 1991), 77. form, and potential energy also have roots in Aristotle’s philosophy. Aristotle uses the term kivnhsi" for any of the three different kinds of motion and sometimes even more generally to include substantial change. “Form” is another basic principle in Aristotelian philosophy, and energy comes in different forms. “Potential,” “potentiality,” or “potency” is the correlative of energeia and entelecheia and from it William Rankine drew the term “potential energy,” which he first introduced into physics in 1853.3 According to Rankine, The step which I took in 1853, of applying the distinction between “Actual Energy” and “Potential Energy,” not to motion and mechanical power alone, but to all kinds of physical phenomena, was suggested to me, I think, by Aristotle’s use of the words duvnami" and enevrgeia.4 The great nineteenth-century physicist James Clerk Maxwell noted Rankine’s introduction of the term and understood it in a remarkably Aristotelian way: Rankine introduced the termPotential Energy—a very felicitous expression, since it not only signifies the energy which the system has not in actual possession, but only has the power to acquire, but it also indicates its connexion with what has been called (on other grounds...