Against top-down accounts Gallagher comments that they fail (amongst other things) to adequately explain the thematic content of delusion. For example, why does the Capgras patient take himself to have an impostor for a wife, rather than (on the basis of his changed feeling in her presence) maintain that he has simply fallen out of love with her? Or why does the schizophrenic person believe that someone else is responsible for their made actions - rather than a brain malfunction? And if what we have to do with are top-down problems in the formation and maintenance of beliefs, it is not clear why the delusional patient is delusional only about some topics.
Against bottom-up theories Gallagher notes that the extravagant delusional narratives that one sometimes finds espoused by schizophrenic persons appear to outstrip anything that could be provided by aberrant experience alone. Against two-factor theories Gallagher urges that they can still have difficulties with the problem of delusional specificity. Against all such theories: we do not yet have an explanation of occasional schizophrenic double-book-keeping.
Here is a helpful passage explaining the relevance of the concept of delusional realities for advancing beyond the positions of the cognitivists (p. 257): 'To consider a delusion to be merely a belief is, as Jaspers suggested, to abstract it from something much richer - something that the delusional subject experiences and lives through. To consider a delusion to be a framework belief or the result of a dysfunctional introspection about something in everyday (external or objective) reality, is not just to remain too cognitive; it may also target the wrong world. The delusion may not be about external or everyday reality, but may be tied to an alternative reality, in the same way that events that take place in a play are tied to a fictional reality.' Gallagher goes on to describe the fundamental problem of schizophrenic delusion as the 'failure to suspend belief in the ontological actuality of the delusional reality' (contrast holding onto the knowledge that you are in the cinema).
What explains the delusional patient's failure to recognise the imaginary character of their delusional experience? Gallagher draws on Naomi Eilan's suggestion that it is an idiosyncratic and strong affective attunement that keeps the patient's locked into the delusional reality. What this attunement is is not explored further. Gallagher's alternative realities hypothesis addresses the double-book-keeping problem: if one can sometimes see the delusion from the perspective of everyday reality, it will be possible to have some irony about it, even if when caught in the delusional reality it is impossible to achieve any such reflective space. The complexity of delusional content is managed by the alternative reality hypothesis too: Gallagher does not say as much, but presumably the delusion is elaborated by the imagination in the delusional mode. The problem of delusional specificity is addressed by the notion of emotional reactions to specific persons and objects. The question of why there tend to be certain themes shared between different people's delusions 'may call for the same kind of answer that we would give to the question of why there are typical scenarios developed in pretend games and imaginary play in childhood, or 'universal' literary themes found in novels, plays, and other media.'
Critical evaluation: Gallagher's hypothesis seems eminently plausible to me. Perhaps the main criticism, which he himself makes of it several times, is that it is not itself an explanation, but rather a framework for explanations as yet to be developed. Another criticism pertains to the use of the notion of different 'worlds'. At one point Gallagher talks of the way that different ways of relating to the world involve us with different affordances. And says that a 'delusion that starts out in a prodromal experience as a simple feeling of alien forces can develop in complexity if there is a different way to be-in-the-world, a different experiential framework, an alternative reality where it can grow and find support.' However this seems to involve a different notion of 'world', since the delusional subject is not in-the-world in a different way but, on Gallagher's earlier hypothesis, in fact in a different 'world'. (Perhaps we could square this by invoking two different notions of 'world': being in-the-world1 in a damaged way leads to one being stuck-in-a-different-world2.)
However there is I think a more serious criticism to be levelled at Gallagher's theory. Which is that it is not in fact any kind of a novel theory, but instead a timely yet unacknowledged rediscovery of just a few aspects of the age-old psychoanalytical conception of delusion as (to mix together my Lacanian and Jungian terminology for a moment) a matter of a powerful conflation of the imaginary and the real occurring under the sway of feeling-toned complexes. In fact the principal notion of the theory - that delusion involves a failure of the subject to hold onto the notion that they are in a pretend mode - that the subject is prone to take their imagination for reality - is I suggest such a fundamental part of good-old-fashioned mainstream psychoanalytical psychiatry that in the past no-one really bothered to articulate it as such. (Delusion, on this conception, is basically a kind of peculiarly clear-headed topic-specific delirium.) Freud's notion of the libidinal decathexis of the external world and the hypercathexis of the inner world is surely principally another way of making the same point about which world or 'reality' comes to seem the 'more real' to the patient. And Jung's 100 year old word association experiments and his subsequent theorising of schizophrenic psychosis (and, basically, all the psychoanalytical work on psychosis since then) clearly made the case for the significance of feeling-toned complexes (i.e. emotionally significant topics / networks of associations which overwhelm the deployment of the reality principle) in the formation and maintenance of delusion.
Many significant aspects of the various largely complementary psychoanalytic perspectives on delusion are of course missing from Gallagher's theory - their focus on underlying disturbance of ego boundaries and late adolescent failures of individuation which reawaken earlier failures to transition from paranoid-schizoid to depressive functioning, the role of massive projective identification and minus k (reverse alpha function) in the establishing of paranoia, the collapsing of symbolism into symbolic equation, the particular significance of sex (drive, orientation and identity), attachment and aggression, etc. This is not a problem, of course, since Gallagher is only aiming to supply the outline of an explanation, and not to actually explain the derivation of particular delusional content. The real value of Gallagher's paper, however, consists not in its providing any kind of a new theory, but just in it returning us to the fundamental phenomenon of schizophrenic delusionality itself, a phenomenon which those rather thin cognitive / doxastic theories which abound today have rather obscured from our psychopathological vision.