Dealing with the changeable and blurry edges of living things: a modified version of property-cluster kinds

Despite many attempts to achieve an adequate definition of living systems by means of a set of necessary and sufficient conditions, the opinion that such an enterprise is inexorably destined to fail is increasingly gaining support. However, we believe options do not just come down to either having faith in a future success or endorsing skepticism. In this paper, we aim to redirect the discussion of the problem by shifting the focus of attention from strict definitions towards a philosophical framework that allows conceiving of living systems as a natural kind, but whereby natural kinds are not to be defined by fixed necessary and sufficient conditions. We argue for a property-cluster kind approach according to which living systems constitute a natural kind with vague boundaries, capable of changing, and whose members do not need to instantiate every property. We draw from Boyd’s homeostatic property-cluster theory and introduce two modifications, one regarding homeostatic mechanisms and another related to the scientific role of kinds. Thus, our view overcomes some difficulties of Boyd’s theory and we are able to account for the natural kindhood of living things. We also emphasize the most appealing features of our approach for specific research fields and address three objections to this sort of approach.