An Application of the Theory of Definitions to Systematic Principles

Some errors in systematic theory have arisen by attempts to define things instead of words. The abstract concept of the biological species definition is discussed, together with objections to it. The author shows that "homology" is a theoretical term and that phylogenetic definitions of it are not circular. A number of excellent works are available which discuss aspects of the process of classification. But a clear and rigorous explanation of systematic and phylogenetic method, in which the fundamental concepts are fully elucidated and in which the underlying logic is analysed completely, has yet to be published. This lack is understandable, for the abstract fundamentals are deceptively simple, and applying them in practice is often difficult. For the individual systematist, the only solution seems to be a study of numerous examples, asking repeatedly what is the fundamental justification for the method. But paradoxically, there are so many pitfalls of reasoning, however simple the basic principles may be, that attempts to obtain conceptual rigor through analysis of examples often leads to misconceptions. Hence the current controversies over method. One could only resolve the arguments by showing the particular misconceptions upon which each error rests; but this is impractical, since it would require an exhaustive treatment of the entire scope of abstract thought as it applies to systematics. Nonetheless, some of the problems may be readily disposed of without too detailed a treatment, in that they 1 Although the views expressed here are my own, I must express my deepest gratitude for the criticisms and advice of Walter Bock, Barry R. Wilson, Richard I. Johnson, and, especially, Emst Mayr. Support during the period of research was provided by National Science Foundation Grant NSFG19727. derive from errors of reasoning which may be dealt with apart from fundamental principles. It is hoped that this discussion of one source of error will direct the efforts of systematists toward clarification of their thought. Confusion as to the significance of definitions very often leads to mistakes. This is especially true in the application of typological methods to systematics. Indeed, one might argue that insistence upon purely typological approaches to systematics results as a consequence of using the concept of definition in a nonsensical way. It is things which typology seeks to define. But one does not define a thing, one describes it. Definitions apply only to words, not to the things to which the words correspond. They are simply discussions of how words happen to be used, entailing an analysis of the concepts which the words symbolize, or are proposals to use words in a particular way. Usage being conventional, definitions are perfectly precise, exactly because they say nothing empirical. Because both definitions and descriptions are frequently lists of characteristics of things, they are readily confused, and the idea may arise that definitions and descriptions impose the same kind of limitations on the properties of things that they do on the usage of words. The meaning of a word has nothing whatever to do with the practical problem of identifying the things which may happen to fit the definition. However obvious and indisputable it may be, this point is so often