In the past 30 or 40 years there has been much discussion about what factors contribute to readability in texts. In an attempt to characterize factors not measurable by current objective readability formulas, four texts that were adapted for younger readers were compared with their originals to see what kinds of changes adaptors had made and to assess the effectiveness of the changes. A taxonomy of the adaptive changes was developed and possible motivations behind the changes were suggested. Changes were found to be interdependent and influenced by factors such as assumed knowledge of the background, definition of the discourse topic, logical ordering of ideas, and syntactic structure, as well as limitations imposed on passage length, sentence length, and vocabulary choice. Adaptation was found to be most successful when the adaptor functioned as a conscientious writer rather than as someone trying to make a text fit a readability formula. Based on these analyses, the use of readability formulas as guides to writing is not suggested. (Author/MKM)