Given a certain indebtedness that one finds in both Aquinas and Lonergan toward Aristotle, one best attends to developments in meaning as regards essence if one first begins with Aristotle and, from there, move to changes that occurred in Aquinas and Lonergan.
In Aristotle’s Metaphysics (1017a 8-35), one finds two notions of being where, on the one hand, being refers to an affirmation which says that something is true and, because it is true, real and, on the other hand, being also refers to an attributed property where being is identified with essence (the essence of a thing). A thing’s being or its substance is its essence. Cf. Aquinas, Sententia super Metaphysicam, 5, 9, 885-897. For Aristotle, being is form and form is being (in Greek, ousia). Cf. Aristotle, Metaphysics, 7, 17; Lonergan, Insight, pp. 390-391. Why this is so is because form causes being by giving being to matter within the physical or material order of things that is constitutive of the naturally existing world. Cf. Sententia super Metaphysicam, 5, 2, 775: “form gives being, and matter receives it.” Nothing exists apart from its specific determination through the agency of an active principle which is the causality of a form. This form unites itself to what is able to receive it (and so some kind of passive principle is indicated). Matter and form, in joining together to constitute an essence (or what is an essence) constitute a specific kind of being or thing, a specific kind of substance. A “this” instead of “that,” comes into existence. Substance is essence, the “what it is” of a given thing. For a full explanation of the reasoning which led Aristotle to identify substances in terms of essences, see Michael Novak’s, “A Key to Aristotle’s ‘Substance’,” Substances and Things: Aristotle’s Doctrine of Physical Substance in Recent Essays, ed. M. L. O’Hara (Washington, D.C.: University Press of America, 1982), pp. 188-208.
However, as one shifts into Aquinas, one finds a differentiation or a shift in interpretation which effects changes in the meaning of essence. Two points can be distinguished through both refer to changes in understanding which have to do with the meaning or nature of form. In the first change, for a particular reason, it is argued that essences can no longer be viewed simply as substances (as a given union of form and matter). Previously, in the history of thought, for both Plato and Aristotle, forms were seen to exist in an eternal way. But, as the world ceased to be seen as an eternally existing thing, when it was seen as a purely contingent thing (given Christian belief in the world’s creation by God), form lost its primacy as an adequate principle of explanation. A higher, explanatory principle was needed and, for Aquinas, this principle referred to act as an act of existence or being which is to be correlated with an act of rational judgment that affirms whether or not a proposed understanding or meaning is a true understanding or meaning: true or real because of a reduction to first principles of sense and intellect which ultimately specify an extrinsic cause which, in itself, is wholly lacking in any contingency. Cf. Bernard Lonergan, The Ontological and Psychological Constitution of Christ, trans. Michael G. Shields (Toronto: University of Toronto Press, 2001), p. 53. In metaphysical terms, act of existence is to be sharply distinguished from essence or, more specifically and properly, it is to be sharply distinguished from a finite essence which refers to the essence of a contingent thing (as this exists as a union of form and common matter). Cf. Summa Theologiae, 1a, q. 54, a. 3. Understanding a finite essence does not necessarily include understanding its being or existence. Concrete or real being or existence cannot be caused or derived from a nature or essence (with respect to the being of contingent things) even if, admittedly, one can say that natures and essences exist in a qualified sense as hypothetical entities which have been discovered or postulated and which can be employed by minds as explanatory conjugates. Cf. Lonergan, Ontological and Psychological Constitution of Christ, p. 11; p. 53; p. 164. However, an explanatory principle is not a concretely existing being or thing. It lacks the fullness of reality which belongs to the simple existence of concretely existing things although its existence is ordered in some way toward receiving an act of being or existence, an act which is the existence of a given thing or being. As referred or ordered toward possibly receiving an act of existence, an explanatory principle or essence exists as “either as an accident, or as an intrinsic principle of being, or as a possible being, or as a being in the mind.” Cf. Incarnate Word, p. 165. Hence, as an explanatory, second kind of being by which that combines with a first, explanatory being by which that exists in form, nature, or essence (cf. Incarnate Word, p. 157), an act of existence or an act of being adds something to a finite essence by joining with an essence as that by which something is to create a new situation: a being or substance now fully is or exists. A substance or thing is thus not simply an essence. It is not an embodied form. It is not that by which it is but it is what is or that which is (a union which joins essence with act). An Aristotelian understanding of substance is supplanted by a Thomist understanding which associates what something is with the fact of its being or existence. What something is does not always refer to a nature, form, or essence. Cf. Aquinas, Summa Theologiae, 1a, q. 29, a. 4, ad 2; 3a, q. 17, a. 1, ad 7; q. 17, a. 2 & ad 4; Lonergan, Incarnate Word, p. 151; p. 158.
In a second point, while, admittedly, Aquinas retains language which says that form is the cause of being (see Aquinas, Sententia super Metaphysicam, 7, 17, 1667-1668), in other texts, Aquinas engages in an analysis which cognitionally speaks about form as the cause or mover (movens) of understanding. It is that “by which the understanding understands” (quo intelligit intellectus). Cf. Summa Theologiae, 1a, q. 85; Summa Contra Gentiles, 2, 75, 13. It is a mode or a principle of understanding: it is a causa cognoscendi. Cf. Summa Contra Gentiles, 1, 53, 2 & 4: “though this species the intellect comes to be in act.” It is a cognitive tool which is not to be identified with what is understood or known (the id quod intelligitur which exists as the proper object of the human inquiry and the primary object of human understanding, and which also exists outside the mind as that about which questions are being asked). Cf. Summa Theologiae, 1a, q. 56, a. 2, ad 3; 1a, q. 85, a. 2. In contrast with form, the id quod intelligitur is an essence. It is the quiddity or “whatness” of a material thing. Cf. Summa Theologiae, 1a, q. 84, aa. 7-8; q. 85, a. 5, ad 3; a. 8; q. 86, a. 2; q. 89, a. 1. While form and essence both exist as principles of explanation, a real distinction can be drawn between them which helps us understand why a real distinction should be drawn between acts of understanding and acts of conceptualization which proceed from originating acts of understanding. By first understanding a form, one then understands an essence. Form exists as the quo est; it is that “by which something is” (in Latin, quo aliquid est). Cf. Aquinas, In 1 Scriptum super libros sententiarum, d. 8, q. 5, a. 2; De ente et essentia, 4; Sententia super Metaphysicam, 5, 10, 904. From an apprehension of form comes an initial act of understanding. However, as acts of conceptualization proceed from prior acts of understanding, an inner word or definition is formed which unites an abstracted, universal form with a generalized species of matter which is typically referred to as “common matter.” As Aquinas argues in one place, in moving from an act of understanding about what a human being is, one moves from an intelligibility or a form that has been abstracted from a particular instance of human beingness (from “this flesh and these bones” as this exists in a given human being). But, in then moving to a general definition which specifies an essence (a definition which applies to all human beings whatever or however they exist), one joins a universal formal component to a material component which must refer to all possible instances of human embodiment: to “bones and flesh” rather than to “this flesh and these bones.” Cf. Summa Theologiae, 1a, q. 85, a. 1, ad 2. By an analysis which delves into the order of human cognition, form and essence are more clearly distinguished from each other through a form of real distinction which carries over into better understanding about why a real distinction exists between acts of understanding and acts of conceptualization. Essences exist as correlatives of conceptualization; forms, of acts of understanding.
In the more differentiated analysis of Lonergan, essences fall into classifications which distinguish one kind from another. Lonergan speaks about three kinds which appear to be basic (different kinds of essences being determined by different kinds of conceptualization). Cf. Lonergan, Understanding and Being, pp. 165-168. The humanity of a given person is not the same as humanity in general or humanity per se which, as a general property or predicate, refers to what you have if a certain species of intellectual nature is joined to a certain kind of body which is common to all human beings. However, as should be obvious, one cannot speak about the humanity of a given human being in any kind of critical way unless one begins with a critical understanding about what is meant by humanity. In establishing a meaning for humanity as this thus exists in a definition, one takes an abstracted form or idea and one conceives of it or one speaks about it in a way which joins it to a species of common matter. An abstract essence refers to the kind of conception which one has if, in one’s acts of conceptualization, one attends to only those aspects or conditions which are crucial and which must be operative if, in any given instance or experience of material conditions, one is to come to an understanding which grasps a universal significance (as this is present in the apprehension of an intelligible form). If, for instance, one attends to how one has obtained an insight into the circularity of a circle (an understanding about what is the circularity, the intelligibility of a circle), one must attend to relations which exist on a plane surface if one looks at how a center point is related to a circumference through radii that are all equal in length and of an infinite number. Equality in length combined with infinity in number reveal an intellectual necessity (an intellectual necessity which points to a mathematical law) and this intellectual necessity explains why a circle must always be perfectly round. Once this necessity is understood, one has grasped the nature of roundness or the nature of circularity as this exists with respect to a circle. The common matter in this case refers to any size of circle which can be drawn or imagined to exist on a plane surface. From any imagined circular configuration of points and lines on a plane surface, one can come to know the essence of any or all circles. See Lonergan’s Insight: A Study of Human Understanding, pp. 31-37, for a fuller account about how one can move from images or phantasms to a self-transcending act of understanding which grounds an act of conception that is able to generate an explanatory meaning for what exactly is a circle.
On the basis then of an abstract essence, one can take this kind of essence and apply it to particular instances and thus, by such an application, obtain a meaning which refers to a particularized essence. In thinking about the humanity of any given person, an abstract meaning is joined with an instance of individual matter and, from the union of these two principles, one gets a meaning for specific humanity which exists as a function of these two principles in how they interrelate with each other. The humanity of any given person always varies and differs as one moves from one person to another and, yet, the humanity which one person has is not necessarily less than the humanity which another person has. In other words, as one moves from person to person, humanity exists as a concrete variable which changes as persons change in how they live and act. In the transfer or shift which occurs as one moves from an abstract notion of essence to a particularized notion of essence, a reverse kind of return is made to the experience and data of sense. However, as Lonergan notes, if one attends to what Aquinas refers to when he speaks about the formal object of the human intellect (which is being or truth) but what Lonergan identifies as a notion of being (an intention of being) which shapes and moves all human inquiry toward a knowledge of being or truth, a third kind of essence can be identified: an essence which exists in itself as a species of being. Cf. Understanding and Being, pp. 167-168. For examples, Lonergan speaks about “man” or “this man” and not about any kind of humanity which can exist in either an abstract or in a particularized way. In other words, as one thinks about the finality of human understanding (as human knowing undergoes a completion which it receives when affirmative judgments are made), abstract and particularized essences becomes realities or beings in their own right (things or substances which exist in more than a conceptual way) although they do not exist as only as compositions of form and matter. In his day, Aristotle had conceived of substances as compositions of matter and common form. But, in the understanding which Lonergan proposes, it is now possible to identify essences with concretely existing substances (or concretely existing things). In a way, it can be said that Lonergan returns to an earlier association which one finds in Aristotle although with a key difference which refers to an isomorphic relation which exists between human judgment, as a cognitional principle, and act, as a metaphysical principle. Essences are real; they exist as things if constituted by a material component, a formal component, and an actual component.