The likeness argument dominates the dispute over the reality of mental illness. As a matter of fact, no one has yet produced a version of it which achieves what it aims and claims to be able to achieve, namely to answer the question whether or not conditions such as schizophrenia really are illnesses or not. Disputes continue on all sides about which likenesses and differences are to count, and what they are to count for. I have argued that the likeness argument cannot close these disputes, because two of the assumptions it relies upon to do so do not stand up to scrutiny. In particular, the idea that the features which should decide the issue (as the first assumption states), are describable independently of views about the issue (as the second assumption states), is false. They are not; and so the likeness argument must fail. [Pickering 2004: 253]
Why then, does the likeness argument fail to settle the matter? In his book The Metaphor of Mental Illness [Pickering 2006], Pickering argues that it depends on two assumptions both of which can be questioned. He says:
If the likeness argument is to resolve this dispute two things must, I think, be taken to be the case:
that there are features of human conditions such as schizophrenia, which decide what category, or kind, these conditions are a member of, and
that, with respect to the presence or absence of these features, a condition such as schizophrenia is describable independent of the category it is assigned to. [ibid: 17]
The first is a general condition derived from a view of how concepts apply to things. The suggestion is that concepts apply in virtue of conditions having objective features. This stands in contrast, for example, to a view where all such concept application depends on an imaginative human judgement. The second is a more specific assumption relevant to the debate about mental illness. It is that the ascription of features to conditions – putative illnesses – can be made independently of a top down decision as to the illness-status of those conditions.
Pickering suggests that both assumptions can be questioned. Criticism of the first – which he calls the ‘weak objection’ to the likeness argument – typically depends on pressing the role of human interests and values in the formation of human concepts. Nevertheless, as he goes on to concede, for the moment at least, there need be no incompatibility between acknowledging a role for interests and values in setting up a scheme of concepts and its autonomous application.
The ‘strong objection’ turns on questioning the second assumption. Pickering argues that the ascription of features to conditions – putative illnesses – depends on the overall category – illness or not – into which they are placed. The argument for this is piecemeal. In each of three cases – alcoholism, attention deficit hyperactivity disorder (ADHD), schizophrenia – he offers competing descriptions of their basic features manifesting first an assumption that they are illnesses and second that they are not. The behavioural features of alcoholism, for example, can equally be described in terms of moral weakness or of causally determined pathological behaviour. The same data can be equally well interpreted in the light of opposing top-down theories. Arguing that this is a general feature of such contested cases, Pickering concludes that the features themselves cannot be used to determine to which overall category the condition belongs. (He goes on to note that this claim also undermines the first assumption and thus his earlier concession was temporary.)
Now in the past, I thought along these lines:
This criticism is, however, not as successful as Pickering suggests. His central claim is that detectable and observable features of a condition, a putative illness, cannot be described without begging the question of the pathological status of that condition. This is not, however, a surprising claim. If the correct description of the features is taken to imply a pathological status then, trivially, it cannot be independent of the overall status. But even if it merely provides evidential support, Pickering has really only undermined a foundationalist version of the likeness argument, one in which observational data can be established independently of any broader theoretical perspectives. But most accounts of scientific theories now accept the theory dependence of data and an essential holism in theory testing. Most would reject a foundational approach to data, as Pickering himself later reports [ibid: 167]. Rejecting foundationalism in favour of scientific holism does not show that the likeness argument (or some version of the likeness argument) cannot work as part of a broader investigation of illness...
But now I am not so sure. Commenting on the suggestions made by two of our students, my colleague Gloria reported her own thought that the concession Pickering himself makes to a defence of the likeness argument against his own ‘weak objection’ is too generous.
Sticking with Pickering’s objection to the first assumption made by likeness argument theorists, both responses identify the qualm I have. In the case of the debate about the reality of mental illness, Ann makes the point that “There seems to be no reason why anyone should accept the similarities as being more significant than the differences,” and Rina follows this up with the observation that “the role of the observer/categorizer/diagnostician is not in the background” (and again that “human interpretation is definitely not in the background as Pickering argues).” The two points seem to me to be closely related: if we have no independent reason for accepting one set of similarities over another (e.g. anatomical lesions over reduced fertility), then the spotlight is going to turn on the person asserting a preference for one set of similarities in comparison with the dissimilarities. We want to know why he privileges just that set, and my suspicion is that the answer is likely to be circular: the likeness theorist probably privileges that set because he already thinks that mental disorder is an illness (Kendell) or he already thinks that mental disorder is a myth (Szasz). In other words, it seems to me as though these theorists have already decided how to conceptualise mental disorder, and then they set in search of similarities/dissimilarities that would serve the favoured conception. More generally, it looks like any likeness argument is going to depend on a favoured conception of mental disorder, rather than the other way around (i.e. that the likeness argument supports/justifies the favoured conception of mental disorder). This leads me to think that there is a vicious circularity underpinning the likeness argument, at Pickering’s Stage 1, and that this is more devastating to this strategy of arguing for the reality (or otherwise) of mental illness than Pickering realises.
There is surely something right about this. As a matter of fact, authors using a likeness argument strategy to argue either against or for the reality of mental illness have picked different criteria and produced different results. It is hard not to suspect that the criteria are picked for the results they produce. Given the dialectic, how else could the selection be disciplined so as not to be question-begging? My previous thought that Pickering was merely assuming and thus opposing a foundational version of the strategy seems to miss the point. How does that thought address this question (of how illness criteria could be selected without begging the central question of the debate for which they have been selected)?
I have today only two rather poor thoughts. One is that the debate concerns both the reality or not of mental illness as a whole but also the reality of mental illnesses. Whilst it is hard to see how a likeness argument could settle the former debate, it might help on the latter. The kind of question it might settle in the latter case concerns the pathological status of particular traits when, for example, the opposing view might be that the trait is a defence against illness, not part of an illness itself. In such a case, there might be sufficient gap between the general criteria of illness selected and their particular application to a novel case. (Of course, there’s no logical gap. But one’s reasons for adopting the general criteria need make no reference to / explicitly anticipate this particular case.)
Given the distinction between the general and the particular debate, I am not sure that a likeness theorist need even be embarrassed by no non-question begging answer to the first debate (about the reality of mental illness in general). But if so, the other thought picks up on my earlier mention of a ‘broader investigation of illness’. We might ask what we want a concept of illness for, what work it is supposed to do. From that inquiry would come a view of the general criteria and from that would follow a view of both mental illness and illnesses. That is, I think, how Jerry Wakefield sees his project: the idea that there is a failure of biological function plays a deep and partially hidden role in our use of the notion of illness. That connection forged, it can come as a surprise what particular results it has (via a likeness argument). But that connection was not made simply with a view to generating particular results.
PS: Original thoughts here. Yet further - more recent - thoughts here.
Pickering, N. (2004) ‘The likeness argument’ Philosophy, Psychiatry and Psychology 10: 243-54
Pickering, N. (2006) The Metaphor of Mental Illness,