Lecture 3: Arguments for the Existence of the Soul, Part I

What this lecture covers

This lecture develops the physicalist position introduced previously and then begins testing whether there is any good reason to believe in a soul at all. It explains what physicalists mean when they say a person is 'just a body' and introduces the general method, inference to the best explanation, that any argument for the soul has to use, since souls cannot be observed directly.

By the end, you should understand what a P-functioning body is, why the physicalist mind is not simply the brain, and be able to evaluate two early candidate arguments for the soul: that a soul is needed to explain bodily animation, and that it is needed to explain thought and reasoning.

Key ideas

• P-functioning body: the physicalist's person is not just any body but one able to perform person-making abilities (P abilities) such as thinking, communicating and planning.
• Mind is not the brain: physicalists treat talk of 'the mind' as shorthand for the body's P-functioning abilities, similar to how a smile is not an extra object but a way of talking about what lips and muscles do.
• Inference to the best explanation: we're justified in believing in unobservable things, like atoms or germs, when positing them gives the best available explanation of something we already accept, not merely any explanation.
• Reserved terminology: Kagan reserves 'soul' specifically for the dualist's immaterial mind, while 'mind' stays neutral between dualist and physicalist views.
• Animation argument fails: the claim that a soul is needed to explain why living bodies move (unlike corpses) is answered by comparing the body to a machine whose parts have simply stopped working together.
• Purposeful-movement argument fails: appealing to guided missiles and robots, the physicalist argues that purposeful, non-random behavior doesn't require anything beyond physical control systems like a CPU.
• Reasoning argument weakened by computers: a chess-playing computer can be described as having beliefs, desires and strategies without needing anything nonphysical, undercutting the claim that thought alone proves a soul exists.

Walkthrough

Defining the P-functioning body (0:00)

Kagan completes the account of physicalism: a person is a body capable of the P abilities. He distinguishes this from a mere corpse, which has the same physical parts but has lost that functioning.

The mind is not the brain (6:12)

He clarifies that physicalists don't deny minds exist; they just treat the mind as a way of describing the body's functioning rather than as an extra object like the brain. Death, on this view, is the breakdown of that functioning, comparable to a broken stereo.

Inference to the best explanation (13:20)

Since souls can't be observed with the senses, any argument for their existence has to infer them from what they would explain. Kagan walks through the general pattern using atoms, x-rays and germs versus demons as examples, stressing that the winning explanation must be the best one available, not merely a possible one.

Feature F: what would a soul explain? (20:38)

The lecture frames the search for arguments as looking for some feature F of people that physicalism cannot explain, or explains poorly, while dualism explains well. Kagan previews that he will work through several candidates for F and give his physicalist responses to each.

Testing animation and purposeful movement (24:44)

The first candidate feature is the animation of living bodies versus corpses. Kagan argues a broken stereo analogy handles this without a soul. A refined version claims purposeful movement needs a soul, which he answers with the heat-seeking missile and robot examples, though he notes the dualist can push back by asking where a robot's instructions ultimately come from.

Testing thought and reasoning (35:59)

The next candidate is the human capacity for belief, desire and reasoning. Kagan uses a chess-playing computer to show that we readily describe purely physical systems as having beliefs and goals, weakening the claim that reasoning alone requires a soul. He ends by narrowing the argument toward emotion, setting up the next lecture's question of whether a purely physical being could feel.

Before you watch

• This lecture continues directly from Lecture 2's introduction of dualism and physicalism; watch that first if you haven't.
• Recall the P-functioning body concept, since it underlies the physicalist responses given here.

Check your understanding

1. Why do physicalists say the mind is not identical to the brain?
2. What makes an argument an 'inference to the best explanation' rather than just an inference to a possible explanation?
3. How does the broken-stereo analogy answer the claim that a soul is needed to explain why living bodies are animated and corpses are not?
4. Why does the existence of chess-playing computers complicate the argument that reasoning proves the existence of a soul?