Man, at least in a state of ordinary well-being, has the wish not to die. This wish is originally identical with the instinct of self-preservation. Whatever lives seeks to maintain itself, to continue alive, and consequently not to die. Subsequently, when reflection and feeling are developed under the urgency of life, especially of social and political life, this primary negative wish becomes the positive wish for a life, and that a better life, after death. But this wish involves the further wish for the certainty of its fulfilment.
Reason can afford no such certainty.
It has therefore been said that all proofs of immortality are insufficient, and even that unassisted reason is not capable of apprehending it, still less of proving it. Such a certainty requires an immediate personal assurance, a practical demonstration. Immortality was with the heathen philosophers a question in which the personal interest was only a collateral point. They concerned themselves chiefly with the nature of the soul, of mind, of the vital principle. The immortality of the vital principle by Do means involves the idea, not to mention the certainty, of personal immortality.