Logical basis for morphological characters in phylogenetics.

Systematists have questioned the distinction between characters and character states and their alignment with the traditional concept of homology. Previous definitions for character and character state show surprising variation. Here it is concluded that characters are simply features expressed as independent variables and character states the mutually exclusive conditions of a character. Together, characters and character states compose what are here termed character statements. Character statements are composed of only four fundamental functional components here identified as locator, variable, variable qualifier, and character state, and these components exist in only two patterns, neomorphic and transformational. Several controversies in character coding and the use of "absent" as a character state are understood here as a consequence of incomplete character statements and the inappropriate mixing of neomorphic and transformational character statements. Only a few logically complete patterns for morphological character data exist; their adoption promises to greatly reduce current variability in character data between analyses. © The Willi Hennig Society 2007.