Explanatory Power and Classification
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The general explanatory successes of the wave theory did not persuade Brewster, who on many occasions admired the merits of the wave theory in accounting for some optical phenomena, but always insisted that its explanatory power was not good enough to allow it to replace the particle theory. To understand Brewster’s judgment, we need to examine how Brewster and other historical actors measured the explanatory power of the wave theory. During the early nineteenth century, there was a consensus in the scientific community that explanatory power consisted not only in the ability to give accounts for numerous phenomena but, more importantly, for various phenomena. If a theory’s successes were restricted to a few classes, its explanatory power was very limited, despite the number of its explanations. Herschel thus insisted that theories should be evaluated with respect to facts “purposely selected so as to include every variety of case” (Herschel 1831, 208). However, how many different classes of phenomena a theory can explain also depends upon how the subject domain is classified, upon which kind of taxonomy is adopted to provide a foundation for categorization and classification. The measurement of a theory’s explanatory power may vary under different taxonomic systems, especially when a new taxonomic system classifies previously homogeneous phenomena as different kinds, or groups previously different phenomena together into one category. This chapter documents an evolution of optical taxonomy accompanying the dramatic changes of optical theory during the early 1830s. These taxonomic shifts affected evaluations of the two rival theories of light. Without the introduction of taxonomic systems with revolutionary structures, the explanatory merits of the wave theory would have gone unrecognized, and the replacement of the particle theory by the wave theory would have been impossible.
KeywordsMajor Category Wave Theory Particle Theory Optical Phenomenon British Association
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