Classification, typology, taxonomy

Summary The semantic field associated with the term ‘classification’, three main intellectual and/or practical operations, and three different products, can be identified — there being no one-to-one correspondence between operations and products. Through intensional classification, the extension of a concept at a given level of generality is subdivided into two or more narrower extensions corresponding to as many concepts at lower level of generality; this subdivision is obtained by stating that an aspect of the intension of each of the latter concepts is a different partial articulation of the corresponding aspect of the intension of the higher concept. Through extensional classification, the objects or events of a given set are grouped into two or more subsets according to the perceived similarities of their states on one or (more frequently) several properties; subsets may be successively grouped into subsets of wider extension and higher hierarchical level. Through classing, objects or events are assigned to classes or types which have been previously defined, usually by an intensional classification, but possibly by an extensional one operating on a different set. When only one fundamentum divisionis is considered, a classification scheme is produced — usually by an intensional classification. The extensions of each class must be mutually exclusive, and jointly exhaustive. Classes need not be at the same level of generality, and may be ordered. When several fundamenta are jointly considered, a typology is produced. This may be done through either intensional or extensional classification. The underlying category space may be “reduced” or reconstructed through “substruction”. When several fundamenta are considered in succession through a series of intensional classifications, a taxonomy is produced. Specific concepts/terms (such as taxon, rank, clade) are needed to deal with taxonomies. In the final chapter it is argued that the role of classification has been improperly assessed by several different quarters: in particular by those who credit it with ontological capacities and tasks; by those who see classificatory procedures as an old-fashioned activity to be abandoned in favour of more “scientific” measurement; and by those who blame the retarded development of an “explanatory” social science on the undue attention paid to classification by many of the founding fathers of sociology and cognate disciplines. 1. CLASSIFICATION AS AN OPERATION The term ‘classification’ (hereafter simply ‘cl.’) is indifferently used for several different operations and for several different products of such operations. It is also used for those sectors of botany and zoology where classification (as an operation) is most frequently resorted to. By analyzing the formal definitions and implicit acceptations of the term ‘cl.’as an operation, three main families of meanings of that term may be clearly recognized: (a) cl. as an intellectual operation whereby the extension of a concept at a given level of generality is subdivided into several (two or more) narrower extensions corresponding to as