We conclude that all men must die.
Similarly, we do not know certainly--not from real, irrefutable evidence at least--that the soul of any man or woman dead has ever returned visibly to earth.

We conclude, therefore, that none ever will.

There is a difference in the two cases, which throws a slight balance of probability on the side of the ghost.

Many persons have asserted that they have seen ghosts, though none have ever asserted that men do not die.

For my own part, I have had a very wide, practical, and intimate acquaintance with dead people--sometimes in very queer places--but I have never seen anything even faintly suggestive of a ghost.