Coherence of structural and functional descriptions of technical artefacts

Structural and functional descriptions of technical artefacts play an important role in engineering practice. A complete description of a technical artefact involves a description of both functional and structural features. Engineers, moreover, assume that there is an intimate relationship between the function and structure of technical artefacts and they reason from functional properties to structural ones and vice versa. This raises the question of how structural and functional descriptions are related. The kind of inference patterns that establish coherence between structural and functional descriptions are explored in this paper, using the analysis of coherence creating relations of Thagard et al. Explanatory, analogical and practical inference patterns are discussed and it is argued that of these three, practical inferences may be the most important. Practical inferences, however, cannot provide a full underpinning of the coherence of structural and functional descriptions of technical artefacts. The paper ends with the suggestion that any account of the coherence of the structural and functional descriptions of technical artefacts must involve reference to their intentional features.