The inner life of animals
On the axis: Moral circle · an animal's mental life
The whole debate assumes that animals feel something: but can we know it? Descartes saw them as machines without consciousness; how can we be sure there is "something it is like" to be a bat?
Justification
Deprived of thought and therefore of soul, animals are for Descartes mere automata, the famous beast-machine: they neither feel nor suffer in the proper sense, their cries being only mechanical effects. Moral consideration is thereby restricted to thinking beings alone, a strict anthropocentrism.
Discourse on Method, V · Letter to the Marquess of Newcastle, 23 November 1646
Justification
The argument rests on a principle: what I clearly and distinctly conceive as able to exist apart really exists apart, since God could create it so. Now I can conceive my mind, pure thinking thing (res cogitans), with nothing corporeal attributed to it, and body, pure extension (res extensa), with no thought. My essence is therefore to think, and the mind is really distinct from the body, a substance of another nature than the brain. This substance dualism breaks with the Aristotelian soul, form of a body, and at one stroke frees matter for a purely mechanistic physics; yet it bequeaths the problem, which Descartes will struggle to solve, of their union and interaction.
Meditations on First Philosophy, VI
Anchors: Descartes · Nagel
leads to: Can a machine think (The imitation game) · The enigma of consciousness (Minds other than my own)