The main concept of William Morris Davis was to arrange landforms into a cycle of development. His legacy was a concern with historical theory, which lasted until the 1950s (Chorley 1978). Despite claims by some commentators that more recent changes have been essentially incremental (Stoddart 1986), it seems quite clear that there has been a 'revolution' within the science of geomorphology over the last three decades. Following Kuhn (1962), Cohen (1985, p. 41) suggests several criteria by which a revolution may be seen to have occurred: 'these include conceptual changes of a fundamental kind, new postulates or axioms, new forms of acceptable knowledge, and new theories that embrace some or all of these features and others'.