Philosophical
Raven Paradox (Hempel's Paradox)
Does a green apple prove that all ravens are black?
Overview
A paradox of confirmation theory showing that evidence can seemingly support a hypothesis in unexpected ways.
The statement 'all ravens are black' is logically equivalent to 'all non-black things are non-ravens'. So observing a green apple (non-black, non-raven) should confirm that all ravens are black - which seems absurd.