The Return to Form

The role of form in Aquinas’s ontology is to determine structure. Structure, in turn, determines the organization of reality. This is what Aquinas calls a formal cause. As Haldane noted: ‘If realism is to be vindicated, the relevant relationship between the content of a veridical state and its object is one of identity.’[1] It is through an analysis of form that ontological realism and epistemological realism hold together. Aquinas means more by ‘form’ and ‘formal cause’ than the mere arrangement of physical structure of an entity of a natural kind. Substantial form is ‘determinative’ of the essential or sortal properties of a kind. Following Aristotle, the form of a biological kind determines a complex integrated set of metabolic processes concerned with sustaining life, growth, sensation in animals, mobility, and so forth. In the case of non-living primary substances, the function of the form is what ultimately counts for tensile strength, ductility, whether or not it is a good conductor of electricity, and so forth. An individual of a natural kind will have a form-dependent physical arrangement; much more than this, however, arrangement is form-dependent and essential to a specific kind of primary substance. Regarding substantial form, ontological realism argues that there exists a structured world independent of consciousness. The correlative to ontological realism is epistemological realism, which claims that in perception and thought, a human knower is capable of direct awareness of the world and of attaining knowledge of its structure. In the metaphysics and philosophy of mind of Aquinas, both ontological realism and epistemological realism depend on an analysis of form, both substantial forms for sortal properties and accidental forms for incidental characteristics. Representationalism or representative realism is the theoretical rival of epistemological realism, which illustrates the wide gap between Aquinas and Descartes.

What does the analysis put forward in this chapter entail? The following ten propositions follow from the extended discussion developed above:

  • (a) The acceptance of a position of ontological realism. This position holds that there is a pre-existing structure to reality that is independent of mind.
  • (b) The acceptance of a position of epistemological realism. This position holds that human knowers can be directly aware of reality and know its structure. Ontological realism is a necessary condition for epistemological realism.
  • (c) Propositions (a) and (b) entail adopting some form of externalism and a rejection of internalism.
  • (d) Intentionality theory requires that the capacity to know be considered a ‘primitive’ in Aquinas’s ontology. For Aquinas, intentionality is rooted in a set of cognitive dispositions or powers grounded in the substantial form of the knowing subject or cognitive agent. Being a ‘primitive’ does not suggest that no analysis is required. Rather, primitive is an intrinsic, non-acquired, irreducible capacity of a human being. Intentionality is a constitutive feature of a human being.
  • (e) From the texts noted above, Aquinas spells out this characteristic in terms of a knower’s ‘taking on the form of another without matter’, which is the equivalent of esse intentionale in Thomas.
  • (f) This analysis requires that there is an isomorphism of structure between the form of the thing and the form as known in the mind.
  • (g) One must take Aquinas literally here—there is a strict, formal identity of form between the knower and the known. The content of knowing as exemplified in esse intentionale is formally identical with the quality—either sortal or incidental characteristic—exemplified in the esse naturale of the thing.
  • (h) It follows from proposition (g) that the form structuring a primary substance or individual of a natural kind outside is exemplified in that individual. When the form is known in a knowing or cognitive potency, the form is exemplified in that cognitive potency. This second exemplification determines the ‘aboutness’ of the mental act.
  • (i) Aquinas illustrates this formal identity when he claims that ‘Sensus in actu est sensible in actu, and ‘Intellectus in actu est intelligible in actu. What makes knowledge possible is that the form known is identical with the form in the thing. This holds for both sense knowledge and intellectual knowledge. Hence, form as the foundation for isomorphism is the grounding for his ontological and epistemological realism.
  • (j) Efficient causality alone cannot explain the exemplification of the content in a mental act. Hence, formal causality is a necessary condition for perception.

It follows that isomorphism of structure or form is a necessary condition for understanding intentionality theory in Aquinas. The two Latin propositions ‘Sensus in actu est sensible in actu and ‘Intellectus in actu est intelligible in actu denote this isomorphism. The explication of these two propositions is: (a) the sense faculty in perceiving (in actu) is the identical form of the extensional sensible object (in actu); and (b) the possible intellect (intellectuspossibilis in actu) in knowing a set of sortal properties (the essence) is, in principle, identical with the natural kind (in actu) in the external world. The ‘est’ is the ‘is of identity’.

In conclusion, what Aquinas contributes to the contemporary discussion in the philosophy of mind might be articulated in the following set of propositions:

  • (a) a formal identity of knower and known; this is the ‘equivalent value’ of the esse naturale/esse intentionale distinction;
  • (b) an ontological theory of intentionality;
  • (c) a necessary condition in sensation theory requiring more than efficient causality;
  • (d) a denial of the ‘inner theatre of the mind’ model for explanation;
  • (e) an argument for direct realism in opposition to representationalism;
  • (f) the adoption of externalism and a rejection of internalism.

The analysis put forward in this study is rooted in Aquinas’s Commentary on Aristotle’s On the Soul. In the end, this chapter is in agreement with Haldane’s suggestion: ‘in their own ways influential figures such as McDowell and Putnam have been working towards positions very close to that of Aristotle and Aquinas.’48 In a different context, Kenny wrote: ‘I believe as a matter of fact, that the clearest insight into the nature of the mind is to be obtained from the Aristotelian viewpoint.’[2] If this analysis is correct, this explains the subtitle for this chapter: ‘From Aquinas to Brentano and Beyond’, which suggests that this analysis of intentionality theory rooted in Brentano is of more than merely historical interest. Possibly the insights of medieval philosophy may assist philosophers to go beyond Brentano and his successors in the philosophy of mind.

48 Ibid., 42.

  • [1] Haldane, ‘Insight, Inference and Intellection’, 40.
  • [2] Kenny, Aquinas on Mind, 18.
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