Sherlock Holmes and Dr. Watson went on a camping trip. As they
lay down for the night, Holmes said: “Watson, look up into the sky and tell me
what you see”
Watson: “I see millions and millions of stars”
Holmes: “And what do you conclude from that?”
Watson: “Well, astronomically, it
tells me there are millions of galaxies and potentially billions of planets.
Astrologically, I observe that Saturn is in Leo. Horologically, I deduce that
the time is approximately a quarter past three. Meteorologically, I suspect we
will have a beautiful day tomorrow. Theologically I can see that God is all
powerful, and that we are small and insignificant part of the universe. But
what does it tell you Holmes?”
Holmes: “Watson you idiot! Someone
has stolen our tent!”
In the annals of literature, no
character is as renowned for his powers of ‘deduction’ as Sherlock
Holmes. But the way Holmes operates is not generally by using deductive logic
at all. He really uses inductive logic. First he carefully observes the
situation, then he generalize form his prior experience.
We don’t know exactly how Holmes arrived at his conclusion, but
perhaps it was something like this:
1.
I went to sleep in a tent, but now I can see the
stars.
2.
My intuitive working hypothesis, based on analogies
to similar experiences I have had in the past, is that someone has stolen our
tent.
3.
In testing hypothesis, let’s rule out alternative
hypotheses:
a.
Perhaps the tent is still here, but someone is
projecting a picture of the stars on the roof of my tent. This is unlikely,
based on my past experience of human behavior and the equipment that experience
tells me would have to be present in the tent and obviosly isn’t.
b.
Perhaps the tent blew away. This is unlikely, as my
past experiences lead me to conclude that that amount of wind would have
wakened me, though perhaps not Watson.
c.
Etc.
4.
No, I think my original hypothesis is probably
correct. Someone has stolen our tent.
See, It’s induction.
