What is water ?

Putnam’s writings have established as philosophical orthodoxy the idea that substance kinds are identified by microscopic structure. The precise nature of the claim is difficult to pin down to a concise quotable formulation, however, and seems to rest on assumptions about how chemical kinds, typified by water, are understood by scientists and laymen which have not been clearly stated. Not only have the scientific details been severely rationed. Putnam is too quick on the dots in exemplifying the features forming his stereotypes, given the poor general characterisation offered of the layman’s conception. Any attempt to fill out the list soon runs into the problem of discerning how the line is supposedly drawn between ordinary and scientific descriptions. I suggest that microstructure does not play the leading role in individuating chemical kinds that recent discussions presuppose; rather, there is a complexity and variety at the microlevel which is unified only if seen in relation to single macroscopically distinguished kinds. Some aspects of the systematic role macroscopic features of matter play in determining chemical kinds, in particular thermodynamic criteria for sameness of kind, are outlined in section 1. Section 2 addresses the problem of providing a construal of ‘water is H2O’ and relating microto macrodescriptions.