Suppose we are to believe that the soul exists. If the body is extinguished upon death, then is any type of afterlife in which the soul survives impossible? To me, the body is the soul's material basis; the soul is the functioning of the body. Consequently they cannot be regarded as separate since they are but separate names referring to a single object. For example, the soul is to the material basis as sharpness is to a knife; the body is to its functioning as knife is to sharpness. "Sharpness" does not name knife nor "knife" sharpness. Nevertheless, without sharpness, there is no knife; and without a knife, there is no sharpness. I have never heard of sharpness surviving the destruction of a knife; how then can we accept that the soul survives after the body has died? Or is soul something else?

This is a terrific question, even though you must admit that you are assuming all sorts of things: above all that the soul is the functioning of the body, and that the body is extinguished with death. One important tradition in thinking about immortality of the soul refuses to accept the former of these. That is the Platonic tradition, which believes that it can conceive of and define the soul independently of this material functioning. On that tradition, the puzzle you are raising does not come up. However, the tradition that begins with Aristotle does indeed understand the soul as your question assumes, and there are even strains within Platonic philosophy that do the same. Certainly Christianity, with its belief in the resurrection of the body, proceeds with the thought that immortality must be grounded in the body's continued existence. So let's acknowledge that your assumptions are not shared by all theorists on the subject and press on. One question the defender of immortality might...