This chapter aims to make a more detailed analysis of descriptive knowledge. It is concerned with the features of descriptive knowledge which distinguish it from explanatory knowledge than with those which differentiate it from pictorial symbolism in general. Descriptive knowledge is relatively unstable and tends to pass over into explanatory knowledge. This factor of transition is inherent in the character of the descriptive system so that by its own development it tends to become something other than itself. Knowledge can progress only by the rapid acquisition of information. Description represents science in the exploratory stage in which data are being gathered, and in the classificatory stage in which they are being grouped and named. The characteristic feature of descriptive knowledge is its unwillingness to admit hypothetical and theoretical entities, idealizatons, constructs, and fictions into the body of science.