Observing a green apple increases the likelihood of all ravens being black

Sunday, November 30, 2008


Given the proposition
(1) All ravens are black.

the observation
(2) My pet raven is black.

is clearly evidence supporting the hypothesis that all ravens are black.

However, statement (1) has precisely the same meaning as:
(3) Everything that is not black is not a raven.

and the observation
(4) This apple is green.

supports (3) just as (2) supports (1).

Since (3) and (1) are logically equivalent, the observation of an apple that is green supports the assumption that a raven is black.