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levels of ideas which are required for successful civilization, namely, particularized ideas of low generality, and philosophic ideas of high generality. The former set are required to reap the fruit of the type of civilization immediately attained; the latter set are required to guide the adventure toward novelty, and to secure the immediate realization of the worth of such ideal aim.

I am indebted to my wife for many ideas fundamental to the discussion; and also for the great labour of revision of the successive drafts of the various chapters.

ALFRED NORTH WHITEHEAD

HARVARD UNIVERSITY

September 1932