Why We Can No Longer Rationally Believe That Our Intellective Soul is a Substantial Form: On the Degringolade of the Simplicity Argument

The most pedigreed line of thought about mind is the simplicity argument: that the unity of thinking entails the simplicity, immateriality, and immortality of soul. It is widely taken to be a rationalist argument, as opposed to an empiricist or peripatetic argument (see Mijuskovic, The Achilles of Rationalist Arguments), which was completely destroyed by Kant in the First Critique. In this paper it is argued that there is a conceptual connection between the downfall of the Aristotelian conception of soul as substantial form and the downfall of this argument in that in the downfall of the Aristotelian conception of soul it became acceptable to view the functional unity of a material system as constituting a genuine unity per se. This then undermined all philosophical motivation for the postulation of substantial forms. As a result, there was no longer reason for rooting the unity of apperception in the simplicity of a subsistence soul as opposed to some simply emergent power of thinking.