Key to Aquinas’ metaphysics is his distinction between essence (essentia) and existence (esse). De ente et essentia (DEE) describes the essence or nature of an entity as the principle on account of which it belongs to a specific natural kind (as humanity is the essence of man) (chap. 1). Essences (also termed ‘‘forms’’) are either substantial or accidental. A substantial form is the aforementioned principle making a thing to be what it is. Aquinas (controversially) maintained that individuals possess but one substantial form, regardless of the essential predicates we ascribe them (ST Ia.76.3c; Sententia super De anima (In DA) II.1.224). Since entities (conceived as Aristotelian substances) belong to natural kinds through substantial forms, any other forms must belong to entities through accidental modes ofbeing, whose presence or absence does not specify an entity as a member of some natural kind.
Aquinas opposes any Platonist reification of essences, yet insists that essence and existence are distinct principles, with existence making an entity to be in actuality, which is contrasted with being in potentiality. Potentiality belongs to an entity which can be in a certain way but does not currently have that way of being, whereas actuality belongs to what is (Deprincipiis naturae (DPN), chap. 1). Transitions from potentiality to actuality are cases of substantial and accidental change. Substantial change is the generation of one substance following the corruption of another, as when a human becomes a corpse, which is a new type of thing that is human only in an equivocal sense (ST Ia.76.8; SCG IV.81).The matter underlying substantial change is conceived as in potentiality to all forms and thus termed ‘‘prime matter’’ (DPN, chap. 2). Accidental change, on the other hand, involves a substance taking on or losing an accidental form, without itself being corrupted. Thus, generation absolutely speaking (to substantial form) and generation with qualification (to accidental form) require a being in potentiality (matter), nonbeing in actuality (privation), and an actualizing principle (form) (DPN, chap. 1).
To these principles are added agents and ends (DPN, chap. 3). Agents are required as no form, whether substantial or accidental, renders itself to be in actuality, as it would then have to preexist itself. Needed, then, is an agent whose activity accounts for the coming to be of the form. Again, agents (even unintelligent agents) are inclined toward ends, though it does not follow that all agents deliberate. Therefore, change requires four causes: an agent (efficient cause), matter (material cause), form (formal cause), and an end (final cause). As a logically prior antecedent to change, privation is a principle, but does not count as a cause in the strong sense that requires a cause to produce an effect; were privation a cause in this sense, mere lack of form would bring about change.
Also important to Aquinas’ metaphysics is the convertibility of the transcendentals: being, truth, and goodness (Quaestiones disputatae de veritate (QDV) 1.1). ‘‘Being,’’ ‘‘truth,’’ and ‘‘goodness,’’ along with ‘‘thing,’’: ‘‘one,’’ and ‘‘something,’’ comprise the five transcenden-tals: predicates true of all existent things qua existent. Considered absolutely, each being is a thing, or something with an essence, and every being is undivided and hence, one. In relation to other things, every being is itself and not some other, and thus something, and in a sense involving relation to the soul’s appetitive and intellective powers, every being is true and good, good inasmuch as it is desired, and desired to the extent it is a being in actuality (ST Ia.5.5c), that is, a being in actuality with respect to its specific perfections. Truth, on the other hand, is a mode of being involving a conformity of intellect and object when, in cognizing, intellect receives its object’s likeness. Thus, entities are termed ‘‘true’’ in the way food is ‘‘healthy,’’ both predicates signifying a mode of being whereby the subject acts on another. In the case of truth, this action results in an isomorphic (or true) conformity of the intellect with its object (QDV 1.4). In the proper and primary sense, though, something is true to the extent it conforms to God’s divine idea of it (QDV 1.4). This latter sense relates to actuality, for things can fall short of divine ideas to the extent they fail to evidence or actualize the potentialities belonging to their specific kinds. Accordingly, there is a correspondence between actuality and goodness dependent on God’s creative intent. Most properly speaking, a thing is good to the extent it actualizes the potentialities God has determined with respect to its species, and hence the better an entity is, the more in actuality it is with respect to these potentialities.
World History
