First, consider the contrast between those roles or disciplines whose related expertise or knowledge defines the role or discipline and those where the relationship is the other way round. One might think that neurology or physics or mathematics belongs to the former category. What unifies the role or discipline of practitioners is the nature of the knowledge in question. (I must admit to some scepticism about this side of the contrast: that the subject of mathematics, for example, individuates itself, comprises a natural kind, independently of the toil of self-identified mathematicians. I can imagine a need for a sociology of mathematics to explain why branches of reasoning, such as Newtonian fluxions, were counted as properly mathematical. But despite this, it might help demonstrate a scale if not a distinction.)
The distinction is, at least, supported by what seems to be related. Where the knowledge is prior to the role it is more likely to be sui generis. In this case, our understanding of the subject matter of mathematics is not settled elsewhere than by the work carried out by mathematicians. It seems plausible to think that where that is the case, the subject matter of the relevant knowledge can be used to define the role or discipline, rather than the other way round.
On the other side of the distinction, there might be roles such as restaurant proprietorship for which what is known, or needs to be known, is not intrinsically unified. The role gathers together diverse areas of subsidiary knowledge as the knowledge proper to restaurant proprietorship. This might include some of what is involved in cookery, customer relations, tax law etc. To identify restaurant-proprietorship-knowledge, one needs to identity first the role and only then whatever is the knowledge that turns out to be necessary to carry it out successfully. Further, the knowledge so needed isn’t sui generis to this role. It involves the right mix of what is known in other roles by chefs, social psychologists and moral agents, and tax lawyers.
Given that rough contrast of the order of determination of professional role and underpinning knowledge, I think that nursing lies in the second camp. First, one identifies the role – in this case centrally via the caring for patients and health service users, though that would need to be articulated – and only then the knowledge necessary for that. Further, addressing the issue of whether it is sui generis, what is known is the right mix of knowledge taken from other disciplines. The argument for this is empirical: a casual glance at the diversity of the nursing curriculum.
Art or science? A first informal answer to that, again looking at the mix of modules in a nursing undergraduate degree, is both. The sciences of physiology and patho-physiology rub shoulders with communication skills, law and values based practice. But there’s a more interesting answer which starts from the challenge raised by the order of determination and rejection of the idea that nursing knowledge might be a sui generis natural kind: how does one select, from the range of other disciplines, which to draw on when?
(*Picture from the very excellent: http://www.waxoil.com/)