But it seems to me that the likeness argument is in one sense quite trivial in form. (This is not to accuse Pickering’s analysis of the same triviality, I hasten to add. The actual forms of philosophical argument are often quite mundane but it can be a significant contribution to draw reflective attention to how a debate has worked.) It turns on taking a concept to have criteria of application and then seeing whether things meet the criteria and thus fit the concept. So if the likeness argument is ruled out it becomes hard to know how else one might argue (for whether a condition fits the concept of illness or not).
Given this tricky situation, one way one might attempt to argue is by trying to come up with a principled, theoretically driven understanding of the general concept illness (rather than one simply designed or selected to give the right question-begging result when put through a likeness argument). And one way to do that is to ask what one wants a concept of illness for.
I think of this because of an idea that Edward Craig had about knowledge. Philosophers have debated the analysis of knowledge - eg saying its justified true belief or true belief via a reliable process - for a long time without resolution. Craig suggested we think what a concept of knowledge might do for us. His idea was that it a way of picking out trustworthy informants. He then used that as an extra theoretical resource to shape the analysis of knowledge.
So if someone like Jerry Wakefield, just as an example, says that we want a concept of illness to mark conditions which result from a breakdown of biological functions - of what bodily systems were selected for - we could interpret that as not just another move within a likeness argument but rather an attempt to find a principled neutral starting point before the likeness argument is set up.
I think of Wakefield as an example rather than eg Bill Fulford but Fulford could be used in the same way. He might say: we want an illness concept to mark conditions which stop us just doing what we can ordinarily do and thus which excuse us, eg, from work. But whether or not Wakefield's idea works ( I have my doubts), he's a better example in this case of this strategy because one thing he claims - in conversation if not in print - is that people do fall back on his idea.
So in the debate about whether homosexuality is an illness, people actually do ask: but is it a failure of biological function? In other words, he argues that at a deep level, that is part of our concept of illness, whether or not we generally realise it. (It is less clear that in debates about homosexuality, for example, people have actually and inchoately picked up on Fulford’s analysis but that is not to say that Fulford does not in the end have the better account.) And we can then go on to discover whether it applies to mental illness as a whole (ie whether anything can be one) and illnesses in particular.
In fact, the latter idea is difficult because it is hard to determine - especially in mental cases - what the biological functions of our cognitive traits are. Our only epistemic route seems to be the telling of normative Just So stories based on what we find a plausible normative story about how things ought to be. But that does not suggest that this general strategy is not a plausible response to the worries about the likeness argument.
