Dualism
Aquinas’s Hylomorphism
The Soul as the Form of the Living Body
Thomas Aquinas holds that the soul is the substantial form of the body, so a human being is one living thing rather than a mind lodged in a machine. Sensation receives the form of an object without its matter, and an interior faculty, the sensus communis, unifies the senses and makes us aware that we are sensing. Intellect is immaterial but must work through sensory images, and the mind knows itself only indirectly, through its own acts.
Thomas Aquinas
What consciousness is
What we now call phenomenal consciousness belongs to the sensitive life of the embodied animal: sense organs receive the forms of things ‘intentionally’, and the sensus communis integrates them into one perceptual episode. Reflective human awareness adds an immaterial intellect that abstracts universals from sensory images.
Mind and body
Soul and body relate as form and matter, so there are not two substances and no interaction problem. The intellect, however, has no bodily organ, which makes the rational soul subsistent and able to exist apart from the body in an incomplete state.
Mechanism
Reception of form without matter: a sensible form exists naturally in the object and intentionally in the sense. The sensus communis then binds the deliverances of separate senses and registers that sensing is occurring.
Core claims
- The soul is the substantial form of the body, so a human being is one substance and the person is not identical to the soul.
- The intellect can receive the forms of all material things, so it cannot be a material organ, which is restricted to a narrow range of forms.
- Awareness of seeing cannot belong to sight, whose object is color, so it belongs to the sensus communis.
- Against Averroes’s single shared intellect, Aquinas argues that this individual person perceives that he himself understands, which a shared intellect could not accommodate.
Criticisms
Burnyeat argued that Aristotelian philosophy of mind is no longer credible because it presupposes matter already pregnant with mind, while Sorabji defended a physiological reading of sensory change. Saying a sense receives a form intentionally does not explain why the reception has a subjective feel, and applying ‘phenomenal consciousness’ to Aquinas at all is an act of translation.
Implications
- AI consciousness: Unlikely
- Sensory awareness belongs to organized living bodies and the rational soul is directly created by God, so an artifact would lack both. Aquinas’s bodiless angels show cognition without senses, but that turns on how a being is created rather than how it is organized.
- Survival beyond death: Yes
- The rational soul is subsistent and survives death, knowing through species infused by God. Aquinas calls this separated state unnatural and incomplete, so full human life requires bodily resurrection.
- Meaning and purpose: Cosmic/Ultimate
- Humans are made in the image of God, and their ultimate end is the direct vision of the divine essence, reached by the supernatural ‘light of glory’.
- Virtual immortality: No
- Since the person is the integrated body-soul organism and the rational soul comes from God, copying a pattern into a machine would not continue the person.
Related theories
- Aristotle’s Hylomorphism (Foundation)
- Descartes’s Substance Dualism (Contrast)
- Brentano’s Intentionality and Self-Awareness (Influence)
- Jaworski's Hylomorphism (Extension)
Sources
- Summa Theologiae, Thomas Aquinas
- Quaestiones disputatae de veritate, Thomas Aquinas
- Sentencia libri De anima, Thomas Aquinas
- De unitate intellectus contra Averroistas, Thomas Aquinas (1270)
- Consciousness and Self-Knowledge in Aquinas's Critique of Averroes's Psychology, D. L. Black (1993)
- Aquinas on 'Spiritual Change' in Perception, M. F. Burnyeat (2001)
- Aquinas on Human Self-Knowledge, T. S. Cory (2014)
- Aquinas's Theory of Perception: An Analytic Reconstruction, A. J. Lisska (2016)
- Thomas Aquinas on Human Nature, R. Pasnau (2002)
- Aquinas, E. Stump (2003)