Some philosopher has noted that philosophical work is the repercussion of a single, decisive flash, from which a before and after can easily be delineated. Such a flash is certainly observable; but the curious thing is that, as is customary before thirty, it only points the way, the unavoidable path, but does not ensure where it will lead. By thirty, there is no denying it, philosophy is done more or less as literature is done: recording and discussing impressions. These, although true, although decisive, seem to require time to crystallize. In other words: the admirable, impressive confidence with which some white-headed philosophers express themselves is almost never matched by younger philosophers, which seems to suggest that the great philosopher is discovered early on, but is only realized after a long time of maturation.