# Abduction

In addition to deduction and induction, abduction also exists.
Deduction is for a proof, and induction is for an emperical
justification. They don't give you anything new. In contrast,
abduction is uncertain, but it gives you new knowledge.

## Deduction

A.
A -> B.

Therefore, B.

## Induction

A1 -> B1.
A2 -> B2.
...
An -> Bn.

Therefore, A -> B.

## Abduction

B.
A -> B.

Therefore, A might be true. (A is a hypothesis)

### An example

This bean is white.
All the beans from the bag are white.

Therefore, this bean might be from the bag.


To use abduction, you should know how to choose the hypothesis.
First, trim off possibilities by falsifying them. Then choose the
simplest one. This is Occam's razor. The simplest one assumes the
fewest, and is the most likely.

In the last example, you might think the bean is white, because
the bean might be a subject of radioactivity. But it is not simple,
assumes more, and is less likely. So you should choose 'from the
bag' hypothesis, rather than the radioactivity one.

For more information, I recommend Charles Sanders Peirce and Umbert
Eco. "The Sign of Three: Dupin, Holmes, Peirce" by Umbert Eco is a
good introductory book. For examples of abduction, "Sherlock Holmes"
series is good.