 In Conceptual Revolutions, Paul Thagard (1992) retains something of Kuhn’s idea of conceptual transformation and the more specific idea of taxonomic transformation. He distinguishes two kinds of reclassification, in terms of the language of tree structures used in computer science: branch jumping and tree switching. Branch jumping reclassifies or relocates something to another branch of the same tree, e.g., reclassifying the whale as a mammal rather than a fish, the earth as a planet, or Brownian motion as a physical rather than a biological phenomenon. New branches can appear and old branches can be eliminated. Meanwhile, tree switching replaces an entire classification tree by a different tree structure based on different principles of classification, as when Darwin replaced the static classification tree of Linnaeus by one based on evolutionary genealogy and when Mendeleev replaced alternative classification systems of the chemical elements by his own table. Taking a computational approach to philosophy of science, Thagard employs his computer program ECHO to reconstruct and evaluate several historical cases of alleged conceptual revolution and arrives at a tamer conception of revolutionary breaks than Kuhn’s.