 Soon Lusin, Sierpiński and their colleagues were finding extreme difficulties in their work. Lusin was so much in despair that, in a paper of 1925, he came to the “totally unexpected” conclusion that “one does not know and one will never know” whether the projective sets have the desired regularity properties (quoted in Kanamori 1995: 250). Such comments are highly interesting in the light of later developments, which have led to hypotheses that solve all the relevant questions (Projective Determinacy, in particular). They underscore the difficult methodological and philosophical issues raised by these more recent hypotheses, namely the problem concerning the kind of evidence that backs them.