not-raven)". This is a straightforward consequence of the standard definition of implication. But is it not the case that, if A and B are equivalent hypotheses, evidence in favor of B is evidence in favor of A. It follows that every observation of something which is not black and also not a raven is evidence that ravens are black.
But in a deeper conceptual sense, none of it is really satisfactory. It is, unfortunately, not concrete enough to satisfy even the most logistically inclined psychologist. There is a tremendous difference between a convoluted, abstract system juryrigged specifically to avoid certain formal problems, and a system with a simple intuitive logic behind it. An interesting commentary on this issue is provided by the following dialogue, reported by Gian-Carlo Rota (1985). The great mathematician Stanislaw Ulam was preaching to Rota about the importance of subjectivity and context in understanding meaning.