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What is function?

Definitions from the literature

Webster's Dictionary: One of a group of related actions contributing to a larger action; a mathematical entity that assigns to each element of one set at least one element of the same or another set; a quality, trait, or fact dependent on and varying with another. “Function” is comprehensively applicable to the proper or characteristic action of a person, living thing, manufactured or created thing.

[CTT94]: “…the function of a system is identified by the task the system accomplishes or should accomplish…”

  • “…its intended use or purpose…”
  • “…the relation between the goal of human user and the behavior of a system…”
  • “…binding information that relates components to processes in which they take part…”
  • “…abstract characterization of behavior performed by taking into account the purpose of a system, namely, the reasons of actual implementation (focusing on overall organizational principles)…”
  • “…interpretation of behavior that captures typical properties of components in terms of generalized actions performed on substances (e.g. information, energy, mass) flowing through them…”
    • This one seems quite widely accepted. Fil Salustri (2013.07.31 12:46)
  • “…function [is]… more abstract than behaviour and structure…

[SOK96]: ”…largely domain-independent characteristics or behaviors of elements or groups of elements of a design.“

[QG96]: ”…what a design does…“

  • Is function what a design does, or what the product does that the design represents? Fil Salustri (2013.07.31 12:46)
    • We need to be clear about the difference between the function of a design and the function of a product that corresponds to that design. Referring to design here is dangerous.
    • Referring to thing implies that natural objects have function – not sure I'm ready for that.
    • So I suggest artifact.

[UIY96]: ”…a description of behavior abstracted by human through recognition of the behavior in order to utilize the behavior.“

[GS96]: ”…the intended output behaviors of a device.“


  • “functions are subjective: the value and even existence of a function depends greatly on point of view and context - users, designers, and others….” This is certainly true during design. However, once a product actually exists, its role/function can be described quantitatively and objectively. This also relates to affordance.
  • “functions are normative: certain functions are given precedence when describing a designed artefact, even if this does not follow how things are actually used….” This relates to intent/purpose of the product, and is often captured in the name of the product class - table, knife, automobile, etc., are all nouns that name a collection of purposes/functions.
  • “new understanding can come from any category, not necessarily the ones given precedence because they are more easily described (technical vs. social); along similar lines, the characteristics of tangible categories can inform us about the less tangible ones.” That is, there is a holistic appreciation of a product that comes not just from the privileged functions, but from all of them in gestalt.
  • In value analysis, a function is represented by an active verb and a measurable noun. This excludes certain other types of functions that are now recognized as significant for successful products, but that cannot be quantified (yet).
  • TODO Brief summary of what the concept represents.

[VD07]: ”…functions are ascribed by agents relative to purposes those agents assign to items….“ (so-called intentional theories) This seems quite close to affordances.

[VD07]: ”…functions of items are said to be reproduced physical dispositions that causally contribute to their existence.“ (so-called etiological theories) I have no idea what this means.


  • TODO Motivation for use.
  • TODO Purpose of concept/method.

Function can be used as the basis for developing integrated conceptions of product “actions” across a variety of dimensions, including technical, aesthetic, social, and economic dimensions [AEO11]. This reinforces the view that a design engineer's work is richly interconnected with many other non-engineering aspects of product development; this underscores the importance of teamwork with experts from non-engineering fields.


  • TODO Domain of problems that succumb.
  • TODO Describe unbalanced forces that can be addressed.
  • TODO Inputs: what's needed to generate concept / execute method.
  • TODO Examples of typical situations.


  • TODO Generative description of how to instance the concept or perform the method.
  • TODO Describe resolution /deliverables.


TODO Describe consequences and counter-indications.

See Also


[SOK96]. R. H. Sturges, K. O'Shaughnessy and M. I. Kilani. 1996. Computational model for conceptual design based on extended function logic. Artificial Intelligence for Engineering Design, Analysis and Manufacturing, 10:255-274.
[QG96]. L. Qian and S. Gero. 1996. Function-behavior-structure paths and their role in analogy-based design. Artificial Intelligence for Engineering Design, Analysis and Manufacturing, 10:289-312.
[GS96]. A. K. Goel and E. Stroulia. 1996. Functional device models and model-based diagnosis in adaptive design. Artificial Intelligence for Engineering Design, Analysis and Manufacturing, 10:355-370.
[AEO11]., [AEO11]. M. Aurisicchio, N.L. Eng, J.C. Ortiz, P.N.R. Childs, and R.H. Bracewell. 2011. On the function of products. Intl Conf on Engineering Design. The Design Society. (link)
design/function.txt · Last modified: 2020.03.12 13:30 (external edit)