Any educated man who "saw a ghost" or "had a hallucination" called it a "dream," as Lord Brougham and Lord Lyttelton did.

But, if the death of the person seen coincided with his appearance to them, they illogically argued that, out of the innumerable multitude of dreams, some _must_ coincide, accidentally, with facts.

They strove to forget that though dreams in sleep are universal and countless, "dreams" in waking hours are extremely rare-- unique, for instance, in Lord Brougham's own experience.

Therefore, the odds against chance coincidence are very great.
Dreams only form subjects of good dream-stories when the vision coincides with and adequately represents an _unknown_ event in the past, the present, or the future.

We dream, however vividly, of the murder of Rizzio.