 Furthermore, Kuhn (in a move toward Feyerabend’s view) now claims that the same types of difficulties in communication that arise due to incommensurability between members of different scientific communities separated by the passage of time also occur between members of different contemporaneous sub-disciplines that result from scientific revolutions (Kuhn 2000 [1993], 238). This represents a significant change to his original phase-model of scientific advance, and a corresponding shift in his application of the notion of incommensurability. Kuhn no longer represents scientific advance as a linear progression from pre-normal science to normal science, through crisis to revolution that results in a new phase of normal science. Instead, scientific revolutions are compared to the process of speciation in biology, in that they result in branching into sub-disciplines that resemble a phylogenetic tree. The application of the relation of incommensurability is no longer restricted to diachronic episodes of scientific advance in which two theories are separated by a revolution. The contemporaneous sub-disciplines that result from a scientific revolution can also be incommensurable with each other. The incommensurability derives from different training required to master the incompatible kind terms used to state their laws and theories. These shared kind terms cross-classify the same set of objects into different sets of kinds, resulting in mutually exclusive lexical taxonomies that break the no-overlap principle. Moreover, now not only are both processes (scientific progress and biological evolution) similar in that they are not fixed in advance on some set goal (i.e. truth), but driven from behind (i.e. away from anomalies that play an analogous role to selection pressure), but also the incommensurability of scientific theories is presented as analogous to the isolating mechanisms required for speciation (Kuhn 2000 [1991], 94–99).