Peter Geach is a contemporary Christian philosopher. His main thesis is that an afterlife is only plausible if it involves a physical resurrection of persons. Geach represents a religious person who rejects both the notion of survival in the form of a subtle body and a disembodied, immaterial soul. In this way, he tries to reason about a belief that common in the western religious traditions. Christianity in particular emphasizes the resurrection of the body, though this belief is found also in Islam and some versions of Judaism.

A. Geach critically discusses two prominent vehicles of survival

1. Subtle Body Theory: The human person survives death in some material form that is similar to but different from our present physical body. (p.225-226)

2. Disembodied existence: The human person survives death as a wholly immaterial substance, e.g., pure mind, consciousness. (p. 226-230)

B. Geach rejects each of these vehicles of survival

1. If the subtle body model is true, then we should be able to detect such a body through observation or scientific methods. But we have not detected any such body. Therefore, the model is not true.

2. If the disembodied model is true, then personal identity is constituted solely by a person's mental life. But this latter supposition is false. Therefore, the disembodied model is not true.

Geach thinks that personal identity cannot be constituted solely by our mental life because thought always presupposes a thinker who must already be individuated in some manner. Thoughts only attach to a being who is already an individual, but then thoughts can no more be the basis for individuating souls than the marks on or shapes of pennies can be the basis for individuating pennies. (p. 229)

Geach doesn't reject the possibility of disembodied minds or spirits, but he thinks that they cannot be identical to person's who have lived and then died. At best, a surviving mental life of a person would be the survival of only an aspect of the person, not the person himself.

Identity thesis: If person A who died at time t1 is the same person as person B who lives at some later time tn+1, then A=B.

A theory of personal survival would seem to require the satisfaction of an identity thesis. According to Geach, a plausible model of the afterlife must entail a plausible view of what constitutes the identity of a person.

Character-traits are not sufficient for individuation because it is possible for many distinct people to have the same character traits.

Memory is not sufficient for individuation because it is possible for distinct persons to have the same memories.

Geach makes two secondary supporting claims here. First, although we may be strongly inclined to believe that some present person named Jack is the same person as a previously deceased person Jeff because Jack reveals information that only Jeff could have known, Geach thinks that in this circumstance we should revise our views on what can be known and how things are known. Secondly, mediums are supposed to be able to contact the spirits of the deceased and - being controlled or possessed by the spirit of the dead - are able to reveal information that only the deceased could have known. But the medium is on all accounts not the same person as the alleged spirit who is speaking through the medium. So this shows us a possible scenario in which two distinct people can possess the same memories.

Geach thinks that continuity of memory is necessary for identity, but it is not sufficient. Material Continuity is also necessary for personal identity according to Geach.

Supporting argument: Our ordinary intuitions tell us that we regard an old man as the same person as a child who was born many years prior because the old man has material continuity with the child. That is, there is a particular physical organism that persists through time, to which consciousness and a mental life is attached. Material continuity also involves a one-one relation: "one baby grows into an old man, and one old man has grown out of one baby" (p. 232).

Note: Material continuity is not the same as material identity. Two things are materially identical just if they have every physical quality in common. But two things can be materially continuous even if they don't share the same physical qualities. A seed and a plant do not have all the same physical qualities, nor does a baby and an adult man. But they are materially continuous, for one develops out of the other.

Hence, Geach thinks that if person A who died at time t1 is the same person as person B who lives at some later time tn+1, then (I) there must be material continuity between A and B and (ii) A and B must share a significant degree of memories. (Call this Geach's "Identity Condition")

Is there a third possible model of the afterlife which would satisfy Geach's identity condition? Yes. Suppose that person A (with a particular body) dies but a new person B (with a particular body) grows or develops out of A with the same memories as A. B would be the same person as A, and person A would have survived death.

The vehicle of the afterlife here is embodiment, not of a subtle or astral body but an actual physical body. This corresponds to the doctrine of the resurrection of the dead in Christianity, Islam, and some versions of Judaism. These western religious traditions teach that at some time in the future all people will be reconstituted as a unity of mind and body, and that these resurrected bodies are in some way continuous with their prior bodies. (pp. 233-234)

Geach adds that we have no philosophical reason to suppose that from corpses there will arise at some future date a new human body that is materially continuous with a prior corpse. There may even be strong scientific objections to this. But it remains a possibility, and this possibility may be strengthened if there is a God, for a God would have the power to bring about such a resurrection of the dead.

Geach's main point is that personal survival is only possible if resurrection is possible, for only a resurrection model would satisfy the condition of material continuity. Geach is not arguing that this model is likely true, but only that it is more reasonable than the disembodied mind alternative.

Question for further thought: What evidence could there be that the resurrection model is true?

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Note: Geach's comments on reincarnation will be handled when we discuss reincarnation. See reincarnation handouts for this.