questions as to the proportion between phantasms of the living which
coincide with a crisis in the experience of the person seen, and those
which do not, it is obviously necessary to reject all evidence of people
who were ill, or anxious, or overworked, or in poignant grief at the time
of the hallucination. It will be seen later that neither grief nor amatory
passion (dominating the association of our ideas as they do) beget many
phantasms. Our business, however, is with the false perceptions of persons
trustworthy, as far as we know, sane, healthy, not usually visionary, and
in an unperturbed state of mind.

There remains a normal cause of subjective hallucinations, expectancy.
This appears to be a real cause of hallucination or, at least, of
illusion. Waiting for the sound of a carriage you may hear it often before
it comes, you taking other sounds for that which you desire. Again, in an
inquiry embracing 17,000 people, the S.P.R. collected thirteen cases of an
hallucinatory appearance of one person to another who was _expecting_ his
arrival. Once more, it is very conceivable that a trifle, the accidental
opening of a door, a noise of a familiar kind in an unfamiliar place, may
touch the brain into originating an hallucination of a person passing
through the door, or of the place where the sound now heard used once to
be familiar. Expectancy, again, and nervousness, might doubtless cause an
hallucination to a person who felt uncomfortable in a house with a name to
be 'haunted,' though, as we have seen, the effect is far less common than
the cause. All these sorts of causes are undoubtedly more apt to be
prevalent among superstitious savages than among educated Europeans.
And it stands to reason that savages, where one man 'thinks he sees
something,' will be readier than we are to think they 'see something' too.
Yet collective hallucinations, which are shared by several persons at
once, are especially puzzling. Even if they occur when all are in a
strained condition of expectancy, it is odd that all see them in _the same