Introduction to special issue: Reconsidering frege's conception of number

Before launching into the introduction to this issue, we would first like to mention a conclusion of sorts. The end in question is of many friendships; many productive collaborations; many days spent eating good food, drinking good wine (or beer), and talking great philosophy; and an end to a great many other wonderful things. Aldo Antonelli passed away, tragically and too young, on October 11 of 2015, when this special issue was near the end of the long path from initial ideas to eventual publication. We could easily justify dedicating this issue to Aldo based on the role he played in its production. He was involved in various ways from beginning to end, and there is no doubt that the issue would be less 'special' had he not added his insights and intelligence, but most importantly his generosity, to the project at various critical points. But that is not the only reason for the dedication. The editors of, and contributors to, this special issue all have fond memories of long conversations with Aldo - often about the very topics discussed in the essays collected here. We are deeply saddened by the fact that we will not have any more opportunities to talk with him about Frege, logicism, and many other things. Thus, we are not dedicating this issue to Aldo just because he was a good philosopher, but also because he was a good friend.