An idea's genealogy is not the idea itself, and still less does an idea's historical context exhaust its potentialities for meaning. The excavation of sources and influences is then for the historian of ideas not an end in itself; it is more properly the inauguration, not the consummation, of efforts in intellectual history. But genealogical investigation does matter, because its vertical depth can illuminate the contours requisite for horizontal discernment, and because exploring its temporal register can free an idea from artificially inert stasis back into the stream of living reflective activity.