. What sorts of observations could confirm the universal hypothesis that all ravens are black? Carl Hempel proposed a number of simple and plausible principles which had the odd ("paradoxical") result that not only do observations of black ravens confirm that hypothesis, but so too do observations of yellow suns, green seas and white shoes. Hempel's response to his own paradox was to call it a psychological illusion---i.e., white shoes do indeed confirm that all ravens are black. Karl Popper on the other hand needed no response: he claimed that no observation can confirm any general statement---there is no such thing as confirmation theory. Instead, we should be looking for severe tests of our theories, strong attempts to fal...