Those who have advocated belief in immortality have often spoiled their case by arguing for different theories without realizing that they were different. Those who have opposed the belief have been apt to think that when they had disposed of one theory they had done all they set out to do. The first condition for clarity of thought on the subject is therefore to distinguish the different types of theory which have been put forward. This is my primary aim in the following discussion. If, in the course of it, I speak more favourably of one theory and less favourably of others, it must be understood that this bias is incidental to my present theme, which is to examine assertions rather than to assert.