Now, if ordinary ghosts are not of flesh and blood, like the sleep-walking house-maid, yet are as irresponsive, as unconscious, and as vaguely wandering as she, then (if the dead are somewhat) a ghost _may_ be a hallucination produced in the living by the _unconscious_ action of the mind of the dreaming dead.

The conception is at least conceivable.

If adopted, merely for argument's sake, it would first explain the purposeless behaviour of ghosts, and secondly, relieve people who see ghosts of the impression that they see "spirits".

In the Scotch phrase the ghost obviously "is not all there," any more than the sleep walker is intellectually "all there".
This incomplete, incoherent presence is just what might be expected if a dreaming disembodied mind could affect an embodied mind with a hallucination.
But the good old-fashioned ghost stories are usually of another type.
The robust and earnest ghosts of our ancestors "had their own purpose sun-clear before them," as Mr.Carlyle would have said.

They knew what they wanted, asked for it, and saw that they got it.
As a rule their bodies were unburied, and so they demanded sepulture; or they had committed a wrong, and wished to make restitution; or they had left debts which they were anxious to pay; or they had advice, or warnings, or threats to communicate; or they had been murdered, and were determined to bring their assassins to the gibbet.
Why, we may ask, were the old ghost stories so different from the new?
Well, first they were not all different.