It is a commonplace of personal and social experience that, having once secured the conditions of human survival and temporal well-being, men have always turned their curiosities to the hows and whys of the universe and themselves in it. Generally, the results of such investigations have found expression in behavioral and systematic patterns formulated in their speculative learnings and assimilated into the language and culture of their times. These learnings and cultures, no less than the universe and societies of which they are the meaningful expressions, are the products of concrete and unique historical processes. To ignore this essentially historical condition of the emergence and development of human learnings and cultures is to risk sacrificing that all-important criterion by which any subsequent age is able to discern and assimilate the definitive achievements of every prior age and thus avoid the extreme alternatives of wholly accepting or wholly rejecting all of the achievements of any given age. To effect this discernment between the tentative and the definitive in the recorded results of our civilized past would seem, therefore, to require some broad yet genuine appreciation of the variables and the constants, the discontinuities and continuities in the past. It is to contribute something to the large task of that discernment that this analysis addresses itself.