Ex-post-facto statistics 69
no evidence that any of these things exist at all. Statements are
made telling what the things must be like if they do exist, and
somehow we begin to encounter claims made about some of
them. At that point, unknown to the audience, the assumption
of real existence has been slipped in without evidence, like an
ace dropped furtively from the sleeve.
All psychic entities are affected by human emotions, but some of them
are more sensitive than others, and tend to be aroused by fear and
hatred.
(And the same is true of invisible frogs, spotted Saturnians and warm-
hearted Swedes. Before you can start sorting them out, you must first
catch your hare.)Use of the existential fallacy is surprisingly easy. Most audi-
ences will respect your modest claims if you move down from
assertions about all things to claims made for only some of them.
This readiness is the gate through which you can drive a coach
and six loaded with fairies and hobbits, ectoplasm and de-
mentals. The malleability of human nature and the perfectibility
of man went through the same gate long ago.
Ex-post-facto statistics
A statistician has been described as someone who draws a
mathematically precise line from an unwarranted assumption to
a foregone conclusion. It is not quite as bad as that, but there are
innumerable statistical fallacies ready to trap the unwary and aid
the unethical. The fallacy of ex-post-facto statistics is perpetrated
when we apply probability laws to past events.
I drew the ace of spades. It was only a 1 in 52 chance, but it came up.
(The same applied to all the cards, but one had to come up.)