‘Intentional’ is Not Identical with or Reducible to ‘Spiritual’
At the outset, one must realize that Aquinas’s discussion of the concept of ‘mental’ or ‘intentional’ is neither equated with nor coextensive with the concept of ‘spiritual. When Aquinas considers esse intentionale, he is not referring to Ryle’s infamous ‘ghost in the machine. Aquinas does not adopt a Cartesian immaterial mind; in fact, he wrote explicitly, ‘Anima mea non est ego’, which is a strong statement affirming his nonCartesian theory of mind and person. This does not entail that there are no spiritual existents in Aquinas’s ontology. Like most medieval philosophers, Aquinas did talk about God and separated substances (angels and disembodied human souls). Nonetheless, it does not follow that, because a being is capable of intentionality, that being also exemplifies a non-material, spiritual existence. Stump reminds us of this hermeneutical point in discussing Aquinas’s theory of intentionality: Aquinas tends to use “immaterial”, “intentional”, and “spiritual” roughly synonymously to refer to this kind of change or reception of form.’ Nonetheless, Aquinas was aware of this possible confusion of ‘intentional’ with ‘spiritual. In the Summa Theologiae, when discussing how an angel knows, Aquinas distinguishes explicitly between a ‘spiritual existence’ and an ‘intentional existence. This is, sadly, often an overlooked passage when commentators attempt an explanation of intentionality theory by putting Aquinas too hastily into the dustbin with ontological, Cartesian dualism. The following is among the clearest passages in which the distinctions between a ‘spiritual existent’ and an ‘intentional existent’ are spelled out.
When one angel knows another angel, it is through a species existing in its intellect; such an existence differs from the known angel not according to a difference between material and immaterial being, but rather according to the difference between natural (esse naturale) and intentional (esse intentionale). For the angel itself is a form subsisting in natural being; yet its species in the intellect of another angel is different in that, in the intellect, it possesses only an intentional existence. In a like manner, the form of color of the wall has a natural existence; yet the same form in a different medium (i.e., when the color is known) has intentional being. (Summa Theologiae, I q. 56 a. 2 ad 3)
This passage is significant for three reasons. First, Aquinas mentions explicitly esse intentionale. Secondly, he distinguishes esse intentionale from esse spirituale. While
esse intentionale is ‘immaterial’, it is neither identical with nor reducible to Cartesian substance immateriality. Thirdly, Aquinas notes explicitly that esse intentionale holds when a perceiver is aware of the colour on the wall. This discussion of angelic knowledge and angelic existence—or ‘subsistence’—indicates that esse intentionale and esse spirituale are neither identical nor coextensive. Furthermore, esse spirituale is an instance of esse naturale. An entity with esse spirituale—God, angels, devils, and disembodied human souls—would be part of the furniture of reality. Given this distinction, a human cognitive agent for Aquinas is not reducible to a Cartesian substance dualist position. To repeat: ‘Anima mea non est ego.’
Aquinas’s characterization of intentionality is neither an incidental nor accidental dispositional property or ability found in the human essence. Rather, the built-in characteristic of ‘tending towards’ is a defining ontological structure of this dispositional property. Aquinas writes generally about ‘intention’ in the following way: ‘intention, as the name indicates, means to tend towards something’ (Summa Theologiae, I-II q. 12 a. 1). Aquinas stresses continually that all knowledge implies that the thing known is somehow present in the knower. Accordingly, the set of dispositional properties, which constitutes a knower as a knower, enables the knower to go beyond itself and yet not physically and entitatively become that which it is ‘tending towards’. In discussing the epistemology of Aquinas, Geach wrote the following about the directedness of mental acts: ‘What makes a sensation or thought of an X to be of an X is that it is an individual occurrence of that very form or nature which occurs in an X—it is that our mind “reaches right up to reality”.’
In Aquinas’s ontology, therefore, the immateriality characteristic of a cognitive being—a knower—is an ontological primitive, which is a metaphysical property that grounds the possibility of intentionality. This is an Aristotelian rendition of Chisholm’s ‘funny characteristic’. Aquinas offers further analysis of the claims of immateriality and the basic ‘tending towards’ or ‘aboutness’ property characteristic of mental acts in his Commentary on Aristotle’s On the Soul when he discusses Empedocles’s principal epistemological principle ‘Like knows like’.
-  Thomas Aquinas, ‘Commentary on St. Paul’s First Letter to the Corinthians, 15: 17-19’ in TimothyMcDermott (ed.), Aquinas: Selected Philosophical Writings (Oxford: Oxford University Press, 1993), 192-3.
-  Stump, Aquinas, 528, n. 35.
-  In addition to human knowledge, Aquinas considers both divine and angelic knowledge. However,there is textual evidence that no esse spirituale is identical with an esse intentionale. In addition, the purposehere is to elucidate the principles of intentionality found in the terrestrial human condition. Thus there isno present concern with how disembodied souls, angels, or God might have knowledge.
-  Aquinas differs from the version of intentionality theory spelled out by Sellars, among others.
-  Anscombe and Geach, Three Philosophers, 95.