70 How to Win Every ArgumentWe cannot draw too many conclusions from the low 'prob-
ability' of certain past events. Something has to happen, and if
the range of possibilities is large, the probability of each one
occurring is small. Whichever one occurs thus has a low prob-
ability. The fallacy is committed when we go on to suppose, from
the occurrence of events of low probability, that something
supernatural was operating:/ met my aunt in Trafalgar Square on Wednesday. Think of the hundreds
of thousands going through the square that day, and you'll realize how
unlikely it was that we should meet there. Maybe we are telepathic.
(And the same applies to the thousands of others you met.)The probability of heads coming up four times in a row is only 1
in 16. The same is true of every other combination which might
come up; only one thing is certain, that a 1 in 16 chance will
come up if you make four tosses. The fallacy goes beyond the
evidence, using statistics in an inapplicable way to point to
mysterious influences where none are needed. Ex-post-facto
statistics often appear in speculations concerning the origins of
life and the universe. Exotic calculations are trotted out showing
the incredible unlikelihood that things could ever have happened
as they did:
How lucky we are that our planet has just the right temperature range
for us, and just the right atmosphere for us to breathe. It has to be more
than luck.
(Ten-legged blue things breathing ammonia on the third planet of
70-Ophiuchi are even now saying the same thing.)Similar claims are made of the probability of the right
chemicals coming together to form life. The fact is that in our
universe chemicals combine in certain ways. If they were