The problematic nature of translation arises from two assumptions. First, as we have seen, Kuhn assumes that meaning is (locally) holistic. A change in the meaning of one part of the lexical structure will result in a change to all its parts. This would rule out preservation of the translatability of taxonomies by redefining the changed part in terms of the unchanged part. Secondly, Kuhn adopts the ‘no-overlap’ principle which states that categories in a taxonomy must be hierarchically organised: if two categories have members in common then one must be fully included within the other; otherwise they are disjoint—they cannot simply overlap. This rules out the possibility of an all-encompassing taxonomy that incorporates both the original and the changed taxonomies.  (Ian Hacking (1993) relates this to the world-change thesis: after a revolution the world of individuals remains as it was, but scientists now work in a world of new kinds.)