Functional reasoning is regarded as an important asset to the engineering designers’ conceptual toolkit. Yet despite the value of functional reasoning for engineering design, a consensus view is lacking and several distinct proposals have been formulated. In this paper some of the main models for functional reasoning that are currently in use or discussed in engineering are surveyed and some of their differences clarified. The models included the Functional Basis approach by Stone and Wood [1], the Function Behavior State approach by Umeda et al. [2, 3, 4], and the Functional Reasoning approach of Chakrabarti and Bligh [5, 6]. This paper explicates differences between these approaches relating to: (1) representations of function and how they are influenced by design aims and form solutions, and (2) functional decomposition strategies, taken as the reasoning from overall artifact functions to sub-functions, and how these decomposition strategies are influenced by the use of existing engineering design knowledge bases.

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