In my study are two large file cabinets. One of them holds copies of correspondence accumulated over thirty-odd years. Among the thickest file folders is one labelled "Felix O." From time to time I clean out this file cabinet, filled with the flotsam and jetsam of years past. But the Felix file has survived all the annual purges, and for good reason. I reread its contents every year or so, and always with appreciation and profit. For it is full to overflowing with carefully typed letters gently chiding and correcting me for my attempts to analyse "power" and other political concepts from an "ordinary language" perspective, for relying too readily on claims about the "essential contestability" of political concepts, and various other errors of my youth. Those letters also thank me – more generously than justly, I now think – for my critical comments on his work.