Lecture 4: Plato's Phaedo Introduction; Arguments for the Soul, Part II

What this lecture covers

The lecture opens with a short introduction to Plato's Phaedo, the dialogue the course will read next, explaining its dramatic setting at Socrates' death and how to read Socrates' arguments as representing Plato's own views. It then returns to the ongoing search for a feature of people that only a soul could explain, working through thinking, feeling and creativity using science-fiction and real-world computer examples.

By the end, you should understand why Kagan finds the reasoning and creativity arguments for a soul unconvincing, why the argument from consciousness (qualia) is harder to dismiss, and how the lecture sets up the free will argument that the next lecture will examine closely.

Key ideas

• Reading Plato's dialogues: the character Socrates generally stands in for Plato's own philosophical views, though scholars distinguish early, middle and late dialogues on how closely this holds.
• Chess-playing programs don't brute-force search: the best programs succeed the way strong human players do, by using learned strategies, not by calculating every possible game.
• Reasoning doesn't require a soul: since machines can be described as having beliefs, desires and strategies, Kagan argues that reasoning alone can't prove a soul exists.
• Behavioral vs. experiential feeling: emotions have a behavioral side (acting to avoid danger), which machines can replicate, and an experiential or qualitative side (what fear actually feels like), which is harder to explain physically.
• Qualia: the philosophical term for the qualitative character of experience, such as what it is like to see red, which Kagan treats as a genuinely open problem for physicalism.
• 'Don't see how' is not 'see that it's impossible': Kagan compares consciousness today to explaining plant life in the fourteenth century, arguing that not having a physical explanation yet doesn't mean one is impossible.
• Creativity doesn't require a soul: chess programs, theorem-proving software and music-generating programs producing genuinely novel results challenge the claim that creativity proves we're more than physical.
• The free-will argument (previewed): 1) we have free will, 2) nothing subject to determinism has free will, 3) all purely physical systems are subject to determinism, therefore we are not purely physical.

Walkthrough

Introducing Plato's Phaedo (0:01)

Kagan gives background on the Phaedo, set on the day Socrates is executed, and explains the scholarly convention of treating Socrates' arguments in the dialogue as Plato's own, with caveats about the differences between early and late dialogues.

Reasoning revisited: how chess programs actually work (8:13)

He explains that top chess programs, like strong human players, rely on learned strategy rather than exhaustive search, reinforcing last lecture's point that physical systems can reason without needing a soul.

Could a machine feel? (14:21)

Using science-fiction robots (the Lost in Space robot, Marvin, HAL 9000), Kagan argues it's natural to describe machines as afraid or depressed based on their behavior, but distinguishes this behavioral side of emotion from its experiential, felt side.

Qualia and the limits of physicalism (21:31)

The lecture introduces qualia, the qualitative feel of experience, as a genuine open problem: physicalism currently has no account of how a physical system could have subjective experience. Kagan argues this doesn't prove dualism is right, since not being able to explain something yet is different from it being impossible, but he treats this as the strongest argument for a soul so far.

Creativity and free will (38:05)

Kagan dismisses the creativity argument, pointing to chess programs, theorem-proving software and music-generation software producing genuinely new results. He then lays out the free-will argument in three premises and closes by flagging that the next lecture will examine whether each premise actually holds.

Before you watch

• This lecture continues the series of arguments for the soul begun in Lecture 3; the qualia and free-will discussions build directly on that lecture's reasoning argument.
• No prior familiarity with Plato is assumed, but you should start reading the Phaedo alongside this lecture, as instructed.

Check your understanding

1. Why does Kagan generally treat views expressed by the character Socrates as Plato's own?
2. What is the difference between the behavioral and experiential aspects of an emotion, and why does that distinction matter to the soul debate?
3. Why does Kagan think 'we don't yet know how to explain consciousness physically' is not the same as 'consciousness cannot be explained physically'?
4. What are the three premises of the free-will argument for the existence of a soul, and which premise does Kagan suggest deserves the closest scrutiny?