The influence of individual thinkers upon the stream of philosophy may be likened to that of tributaries that pour into it. Some may flow quietly into the running waters, adding to their volume and creating eddies in the persistent flow. Others may burst into the mainstream as a great fall erupts into a river, moving the very river bed, shifting the sandbanks, creating powerful new currents and undercurrents, and sweeping away familiar landmarks along the banks by their torrent and turbulence. It is then only many miles downstream that the waters of the river subside and flow calmly again. By then it may be barely possible, and perhaps of little interest, to determine which waters originated in which tributary.

—Hacker, P. M. S. (Peter Michael Stephan),
Wittgenstein’s Place in Twentieth-Century Analytic Philosophy
Blackwell Publishers Inc. (1996)