At Brains: A dialogue on Philosophy of Mind and Related Matters Richard Brown asks the question:

What is striking (to me) about these stories, besides the overal ‘cool factor’ of space stuff, is that these scientists clearly do not think that life is multiply realized. They are looking for planets of about this size (Earth) with water and land masses (Jupitar is ruled out, Mars is in) and they seem to implicitly assume that life on other planets (if we find it at all) will be simple stuff like bacteria. Does this represent a serious flaw in their strategy? I don’t think so. We don’t really have any reason, except our imagination and intuitions, to expect life elsewhere in the universe to be other than carbon-based and water dependent. This makes me wonder why philosophers have such strong intuitions about multiple realizability… [Richard Brown at Brains]

Well…science is nothing if not pragmatic. Millions of years of evolution have equipped us with pattern determination capabilities with biases. Thousands of years of science have augmented these capacities with even more selective sensitivity (or focus - this is not a pejorative remark). Meanwhile, multiple realizability is a concept that has emerged from a history of attempts to devise context-independent logics. These two histories are divergent. Pragmatically, scientists would be crazy to look for things about which they have no intuitions - this is expensive science after all. Any demonstration that the formal representation of a living process had (logically) “near” neighbours is hardly likely to impress someone who has to do the hard work of looking for actual realisations.

No-one (to my knowledge) has ever made sense of the concept, “nearby”, in possible-world semantics. However, fitness landscapes are another matter. On a fitness landscape the concept of “nearby” actually means something. Things can be nearby but unreachable. Perhaps we should distinguish strong from nuanced intuitions about multiple realisability (MR). That way we can support MR but take our cues about reachable space from emprical research. Most philosophical debates about multiple realisability pay no attention to the constraints involved in the material genesis of systems so it’s hardly likely that they will converge with contextually embedded scientific research programmes (where the context includes the methodologies, technologies, pedagogies and institutions as well as the object of the science).

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