Good point but take it one step further: why would a ghost require a body or at least something that looks like one? If a spectre is just the spirit of a person - so to speak their condensed personality - wouldn't it be just that? A spirit in the literal sense, I mean: a disembodied entity?
And, following that line further: wouldn't that mean that a spirit could only be sensed but would be completely invisible, rendering all corporeal (clothed or otherwise) apparitions frauds or at least something completely different from a spirit?
If so, what different thing could that be? Could it perhaps be a sort of afterimage, like the ones you get when you look at a bright object for too long? That would account for it wearing clothes.
So maybe these "ghost sightings" are really just a sort of afterimages of the memory. A very vivid recollection we have of someone.
But what about the ghosts of persons we never knew?
Perhaps in such cases our subconscience adds images that it believes to fit best and in that process might even get a few hints from the spirit itself. That'd for example account for my sis meeting the ghost of a charlady (not only dressed but complete with vacuum cleaner!) in a student hall in Leicester. She might simply have seen what she expected to see / what fit the environment best and learned only two days later that the person she had seen had been dead for several years.
(According to her it was a very nice and friendly charlady, so don't be scared if you happen to study at Leicester Uni).
