Lecture 7: Plato, Part II: Arguments for the Immortality of the Soul

What this lecture covers

Having introduced Plato's theory of Forms in the previous lecture, Kagan turns to the heart of the Phaedo: Socrates' arguments that his soul will not only survive his body's death but exist forever. The lecture explains why this needs separate argument even for a dualist (since the soul could still die along with the body), then reconstructs and critiques three of Plato's arguments in turn.

By the end, you should be able to state each argument's premises, explain Kagan's objection to each, and see how each new argument responds to the weaknesses of the one before it.

Key ideas

• Why immortality needs its own argument: even if the soul is a distinct, non-physical thing, interactionist dualism leaves open the possibility that it is destroyed at the same time as the body.
• The argument from the nature of the forms: forms are eternal and non-physical, and only the eternal/non-physical can grasp the eternal/non-physical, so the soul (which grasps forms) must itself be eternal and non-physical.
• 'It takes one to know one' fails as a general rule: Kagan objects that this premise is false in general (zoologists aren't cats, doctors studying corpses aren't dead), so Plato needs a special reason it holds for forms, which the dialogue doesn't supply.
• The argument from recycling: things are made of pre-existing parts that outlast them (like a car's parts), so if the soul is one of our parts, it should exist before birth and after death.
• Recycling doesn't cover every part: Kagan objects that not every part of something existed before it or survives it (a heart is created with the body and decomposes with it), so recycling alone doesn't show the soul is a 'recycled' part.
• The argument from recollection: we can only be reminded of something, like a photograph reminding you of a friend, if we were previously acquainted with it; since nothing in this world is a perfect form, our ability to think of perfect forms must come from acquaintance with them before birth.
• Kagan's objection to recollection: it isn't obvious we need direct prior acquaintance with perfection to think about it; we might simply extrapolate toward 'perfectly straight' from imperfect straight things encountered in this life.

Walkthrough

Why the soul's existence doesn't guarantee immortality (0:01)

Kagan recaps Plato's metaphysics (eternal, non-physical, unchanging Forms) and explains the worry raised by Socrates' friends: maybe distancing the soul from the body should stop short of full separation, since bodily death might take the soul down with it.

The argument from the nature of the forms (14:24)

Kagan reconstructs the argument in three premises and identifies its weak link, the claim that only the eternal/non-physical can grasp the eternal/non-physical. He argues this 'like knows like' principle is false as a general rule, using zoologists, doctors and cross-cultural scholars as counterexamples.

The argument from recycling (24:38)

Using the analogy of a car built from parts that existed beforehand and get reused afterward, Kagan presents Plato's claim that the soul, as one of our parts, should likewise predate birth and outlast death. He objects using the example of the heart, a body part that neither predates the body nor long outlasts it, showing that recycling doesn't apply to every part.

The argument from recollection (32:51)

Kagan explains how being reminded of something (like a photograph reminding you of a friend) requires prior acquaintance with it, then reconstructs Plato's claim that since nothing in this world is a perfect form, our capacity to think about perfect forms must come from acquaintance with them in a prior existence. He closes by questioning whether direct prior acquaintance is really necessary, or whether we might instead extrapolate toward perfection from imperfect examples encountered in this life, a question the next lecture will pursue.

Before you watch

• This lecture builds directly on Lecture 6's introduction of Plato's theory of Forms.
• Continue reading Plato's Phaedo alongside this lecture, since Kagan is closely reconstructing its arguments.

Check your understanding

1. Why doesn't establishing that the soul exists and is non-physical automatically establish that it survives the death of the body?
2. What is Kagan's objection to the premise that 'the eternal and non-physical can only be grasped by the eternal and non-physical'?
3. Using the heart as an example, explain why the argument from recycling doesn't show that the soul must be one of our pre-existing, surviving parts.
4. What role does prior acquaintance play in Plato's argument from recollection, and what alternative explanation does Kagan suggest for how we can think about perfect forms?