QuestionsShould we fear death?The soul survives: the argument from affinity
Should we fear death?The soul survives

The soul survives: the argument from affinity

The affinity argument

Plato c. 428 BC · c. 348 BCBeyond appearances, the eternal Forms.
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What it claims

The soul is entirely indissoluble, or nearly so, whereas the body is quickly dissolved.

Why

What is composite can break apart; the soul, invisible and thinking, resembles what is simple, while the body quickly dissolves.

In short

"The soul survives: the argument from affinity" is an argument by Plato (Phaedo, 78b-80b) on the question "Should we fear death?" (answer: the soul survives). Its claim: The soul is entirely indissoluble, or nearly so, whereas the body is quickly dissolved. According to AskPhilosophy's logic check (Z3 solver), the argument is valid only if one grants a premise the author leaves unstated (P5). AskPhilosophy presents 3 objections, 2 of them with a documented reply, and the original text behind each premise, checked word for word.

Phaedo, 78b-80b
Valid with an implicit premise

In his prison cell, Socrates asks which things can come apart and which cannot. The soul, he says, resembles what is invisible, divine and simple, so what does not come apart. The body resembles what is visible, mortal and composite. The conclusion is cautious: the soul is indissoluble, or nearly so.

P1What is composite can come apart into its parts. What is not composite is the only kind of thing that cannot undergo this.
P2What always stays the same, and is grasped only by thought, is probably not composite. What constantly changes and can be seen or touched is composite.
P3The soul is invisible: it therefore resembles the invisible more than the body does, and the body resembles the visible more.
P4The soul resembles the divine (what rules), and the body resembles the mortal (what obeys).
P5 · implicit premiseA thing that resembles to the highest degree what does not come apart does not come apart either, or hardly at all: resemblance passes the property on.
Therefore the soul is entirely indissoluble, or nearly so, whereas the body is quickly dissolved.

click a premise to reject it

If you accept every premise, logic forces you to accept the conclusion. So the debate is about the premises.
Checked by a logic solver: the premises cannot all be true while the conclusion is false.
Without the implicit premise: Without P5, the computer finds a case where the soul resembles the invisible and the divine and yet comes apart like the body: resemblance gives nothing more.
Without P5, the premises only say that the soul resembles the invisible and the divine. One must add that resembling what does not come apart is enough not to come apart. Socrates takes this step carefully himself: he says "or nearly so", not "surely".
Analogy. From far away a cloud looks like a mountain, but it does not last the same way. Plato thinks, on the contrary, that for the soul resembling the indestructible goes as far as sharing its solidity.

Objections

3

Each objection is a conversation: click to see who replies and where the debate stands.

S
Simmias (in the dialogue) attacks premise 5

The harmony of a lyre is invisible, bodiless, beautiful and divine, while the lyre and its strings are material and mortal. Yet if the lyre is smashed, the harmony disappears. If the soul is the harmony of the body, it perishes with it, however divine it is.

Platon replies
Socrates (Plato's character) Socrates' reply (Plato's character)
A harmony cannot lead the elements it is made of: it can only follow them. Yet the soul leads the body. So it cannot be a harmony of the body.
The debate goes on (our summary) In the dialogue, Simmias has nothing more to say against it, but he keeps a doubt because of the greatness of the subject and human weakness (107a-b). Socrates answers that the first assumptions should be examined more closely. Plato's text does not say that Simmias is convinced.
Where the debate stands (our summary)Today, many philosophers think the soul-as-harmony theory lives on in other forms (the mind as a function or organisation of the brain). The core disagreement is whether an organisation can outlast the matter it organises. Our summary: an open question.
C
Cebes (in the dialogue) attacks the conclusion

Suppose the soul outlasts the body. It may be like a weaver who wears out many cloaks: a cloak is still whole when the weaver dies, but that does not prove the weaver is alive. Nothing proves that the soul does not wear out over many lives and perish in its last body. "Nearly indissoluble" is not enough to stop fearing death.

Platon replies
Socrates (Plato's character) Socrates' reply: the final argument, from the Forms (102a-107b)
At the end of the dialogue, when death comes to a man, the mortal part of him dies, but the immortal part withdraws unharmed and gives way to death.
The debate goes on (our summary) Our summary: Socrates gets there by a different road from affinity. The soul always brings life with it, as fire brings heat. It therefore cannot receive the opposite of life, death. What does not receive death is deathless, and if the deathless is also imperishable, the soul cannot perish (105c-106e). So the reply to Cebes no longer rests on resemblance alone. In turn, it depends on the theory of Forms, which not every reader shares.
Where the debate stands (our summary)The core disagreement concerns the theory of Forms on which Socrates' reply depends, and the step from "does not receive death" to "cannot perish". An open point: no widely accepted answer.
David Hume 1777 · attacks premise 3

In his essay "Of the Immortality of the Soul", published after his death (written around 1755), Hume relies on experience: thought is born, grows, weakens and fades with the body (childhood, illness, old age, sleep). This suggests that the soul depends on the body rather than being foreign to it. Saying that the soul resembles the divine does not change what observation shows.

no reply
No reply possible: objection raised in 1777, after the author's death (-348).
Where the debate stands (our summary)Defenders of survival (dualists) answer that the body may be a condition of thought without being its cause. Materialists mostly keep the dependence argument. The core disagreement is whether the observed dependence proves identity. An open point, our summary.