James Griesemer and his collaborators have developed the notion of “scaffolding” as a way to think about complex interactive processes such as embryonic development, evolution, social institutions, or the psychology of learning. A scaffold is anything that facilitates the development of something else by lowering the costs involved for the relevant actors. The typical example is the wooden framework assembled under a stone bridge or arch while the structure is being built.. The frame scaffolds the structure by taking the weight from the stones until the keystone is fitted into the gap between the remaining stones and the structure can support itself.
The notion of scaffolds is useful for a number of reasons I won’t get into here— I’ll leave that to Griesemer’s upcoming paper on the topic. But what it got me thinking about was that concepts can be defined functionally, by what they do or have the capacity to do, rather than by their structure, composition, or other attributes. This is not an intuitive notion, but it can be illustrated with examples in world of manufactured parts.
We commonly think of springs as coiled pieces of some flexible material, usually metal. But there are other kinds of springs such as leaf springs which are made from flat sheets rather than coils. The definition of ‘spring’ comes from what they do: hold energy under physical deformation, and then provide that energy back after returning to their previous shape.
Another example: valves; there are many kinds of valves, needle valves, flap valves, gasket vales, and others. These different varieties of valves do not necessarily resemble each other in structure, nor do they need to be made from the same kinds of material. The important part of being a valve is allowing and blocking the flow of a fluid, which can be done through a number of different mechanisms.