Thanks very much for your 'reading list', Haines! I'll have a look into those papers as soon as I have time (which may, unfortunately, mean never -- I am not paid for studying functional explanation and the work I am paid for takes most of my time). 


In my view the notion of function with which Cummins (1972) is concerned is central to biology and the kind of explanation he calls 'functional analysis' or 'functional explanation' is one of the four main kinds of explanation in biology. It is however not the only kind of biological explanation that appeals to functions. In fact, most biologists would call Cummins-like explanations 'causal explanation' and use the term 'functional explanation' to refer to another kind of reasoning, one that is more like Hempel's 'functional analysis'. 

I coined the term 'design explanation' in 1995 to refer to the latter kind of reasonings after discovering that philosophers were confused by my use of the term 'functional explanation'. I sought for an alternative close to the language of working biologists, in a time when they frequently talked about ‘design considerations’ and ‘alternative designs' when discussing non-historical requirements on form, structure and organization. When I coined the term nobody in my country paid attention to the intelligent design movement in the USA, so I had no idea that the term 'design explanation' would be associated with intelligent design.

I call a property of a system organized if that property critically depends on the arrangement of the parts of that system and the timing of their activity in addition to the composition and the character of the parts (this notion of 'organization' is derived from Wimsatt's notion of 'emergence' in ‘Aggregativity: Reductive Heuristics for Finding Emergence’, Philosophy of Science, 64, pp. S372-S384, 1997). 'Design' is just another word for 'form of organization'. So my notion of design is independent of intention and does not imply a designer. It makes no assumptions at all about the way in which the organization is generated.

I am very sympathetic to the view that in order for an analysis/piece of reasoning to be called explanatory it must show that the phenomenon to be explained is somehow "necessary" and the article we are discussing in this thread (which is in part a reaction to Mahner and Bunge's "Function and Functionalism") spells out in which sense design explanations show that the phenomenon to be explained is necessary.