ABSTRACT
The last quarter century of the life of the Dewey Decimal Classification (DDC) began with the publication of Edition 17 in 1965 and ended with the publication of Edition 20 in 1989. The two editions are the most dissimilar philosophically in the history of the Classification (Edition 15 [1951] had no philosophical underpinning and can hardly be called an edition of the DDC). This chapter attempts to explain the bases for the dissimilarity.
