Dispositions and Substantial Form
In the Prima Secundae of the Summa Theologiae, Aquinas provides an in-depth elucidation of the concept of disposition, in the sense of ‘acquired disposition’. What twentieth-century philosophers translate as ‘disposition’ Aquinas often rendered into the Latin as ‘habitus’. Nonetheless, even though Aquinas did have the term dispositio in his philosophical lexicon and used this term in his discussion of habitus, Kenny is probably correct in interpreting dispositio as a ‘state’ rather than as an ‘acquired disposition’. Nonetheless, the meanings are commensurate.
Considering the example of the beginning student and the Hungarian language professor, since both have Dispositions-1, both are alike essentially. As human beings, they both generically differ from a slab of marble or an oak tree. Disposition-1, therefore, is a generic-level disposition whose function is to acquire further dispositions. These further dispositions are instances of Disposition-2/Actuality-1. Therefore, the possession of Disposition-1 level properties ultimately distinguishes knowers from non-knowers at the ontological level. These generic dispositions permit the possibility of knowledge for a human being and preclude such a possibility for an oak tree or a marble slab. This distinction regarding knowers, however, only applies to the disposition to acquire conceptual capacities. Later in this chapter, the discussion of sensation puts forward the claim that a sensation-disposition is an instance of Disposition-2/ Actuality-1. Since sensation is also a case of knowledge, the possession ofDisposition-1 capacities in the cognitive or conceptual realm alone is what distinguishes human knowers from other knowers. What Aquinas calls ‘brute animals’ lack this cognitive capacity. Human beings are those knowers who have the innate ability to acquire intellectual dispositions, which is another name for concepts. This is the ontological characteristic that determines the possibility of intentionality at the conceptual level. Hence, the possession of a set of generic-level dispositional properties of a Disposition-1 nature distinguishes human knowers from other entities in the following manner:
- (a) from other knowers like dogs and raccoons, which have only sense knowledge;
- (b) from other living entities like oak trees and mushrooms, for which the acquisition of any kind of knowledge is logically impossible;
- (c) from non-living entities like marble slabs and chunks of coal, which lack any foundation for what Aristotle would call the possession of a ‘soul’.
In human beings, Disposition-1 capacities constitute the principal content of a substantial form; a substantial form is the ontological ground or foundation for a generic set of dispositional properties, which accounts for nomic universal propositions. There is a synthetic necessary relation between those constitutive properties and individuals classed under them. These are essence-determining sortal properties. The set of synthetic necessary properties accounts for the specific content of a natural kind. One of these capacities is the Disposition-1 ability to acquire further dispositions on a conceptual level. Hence, this dispositional property is a constitutive cognitive capacity. It is a built-in ability to acquire a further ability. This ability is complex in that it is further broken down into the intellectus agens and the intellectus possibilis.
In the foregoing analysis, Aquinas suggested a two-fold and dual level ontological structure to the epistemological dispositions. Disposition-1 would be that dispositional property which on the conceptual level generically distinguishes a knower from a non-knower. Disposition-2/Actuality-1, on the other hand, is a type of dispositional property, which would distinguish various knowers from one another insofar as each would have different acquired dispositions. For instance, while both Smith and Jones are human beings, and a fortiori have the same set of Disposition-1 properties common to the substantial form of human nature, nonetheless Smith may have mastered Riemannian geometry and Jones medieval French. Assuming that Smith does not know medieval French nor Jones Riemannian geometry, each person has an acquired disposition that the other lacks. In Aquinas’s terminology, the acquired disposition—Disposition-1/Actuality-2—is a conceptus or habitus.
-  These categories in Aquinas’s philosophy of mind will be discussed in more detail later.
-  A detailed analysis of an acquired disposition pertains to concept formation and the relation betweenconcept and phantasm. For an instructive account of Aquinas on concept formation, see Kenny, ‘Intellectand Imagination in Aquinas’; Kenny also treats these issues in his later work on Thomas. See also the first40 pages of Geach, Mental Acts.