Delusion Formation through Uncertainty and Possibility-blindness

Algunos autores han intentado considerar los delirios como certezas –entendidas en el sentido de Wittgenstein– debido a las similitudes que parecen existir entre sus respectivos estatus epistemológicos. Sin embargo, dicho intento ha sido criticado con agudeza, entre otras razones, porque el contenido de los delirios choca frontalmente con el contenido de las certezas, por lo que los delirios no pueden ser comprendidos debido a los cambios en las relaciones de significado. Pero es evidente que, aunque los delirios no se puedan contemplar como certezas, muchos delirios afectan de un modo u otro al sistema de certezas del paciente. Partiendo de esta base, no es descabellado pensar que dicha influencia pudiera ser también recíproca: en otras palabras, parece sumamente recomendable analizar si algunos delirios se podrían contemplar como el resultado de variaciones en certezas. En este artículo llevo a cabo dicho análisis al intentar mostrar que el origen de algunos delirios pedestres y severos puede ser hallado en lo que llamaré “ceguera a posibilidades” e “incertidumbre”, términos que he desarrollado teniendo en cuenta la obra del filósofo Ludwig Wittgenstein.


Introduction
Although the hundredth anniversary of the publication of Karl Jaspers' General Psychopathology has recently been celebrated, there is no doubt that this classic of psychiatry, which became the basis of psychopathological phenomenology, continues to be relevant to contemporary psychiatry and psychopathology. A clear example of this can be found in the fact that his definition of delusion as a false belief held with incorrigible certitude despite the great deal of objective evidence of its falsity 2 turns out to be very similar to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV-TR) definition, which reads as follows: "A false belief based on incorrect inference about external reality that is firmly sustained despite what almost everyone else believes and despite what constitutes incontrovertible and obvious proof or evidence to the contrary" 3 . But delusions manifest themselves in very different ways, which has generated criticisms of each component of this definition. Thus, it has been argued that delusional beliefs are not necessarily false, based on inference, referred to external reality, held with complete certitude, contrary to compelling evidence, or regarded as completely implausible by most of one's cultural peers 4 . These criticisms seem to have influenced the new description of delusions which appeared later in DSM-5, where they are considered as "fixed beliefs that are not amenable to change in light of conflicting evidence" 5 . Even though the presumed necessary condition of delusions that has been most discussed is their being a belief 6 , they are still classified as such in the DSM-5.
As regards the debate about the doxastic nature of delusions, it has taken multiple directions 7 . One of those research directions has led authors to analyze to which extent delusions could be regarded as beliefs in framework propositions, that is, as certainties in Wittgenstein's sense 8 . Indeed, delusions and certainties seem to show striking similarities in their epistemological statuses, for both of them "are treated as the background assumptions needed for there to be any testing of the correctness of propositions at all" 9 , to which it should be added that they are resistant to contrary 2 Jaspers, K.: General Psychopathology, Chicago, University of Chicago Press, 1963. 3 American Psychiatric Association: Diagnostic and Statistical Manual of Mental Disorders (4th ed.,text rev.), Washington, Author, 2000, p. 821. evidence just because of this basic framing role 10 . As a result, it is expected that the rejection or acquisition of a certainty would have the same effect as the rejection or acquisition of a delusional belief 11 . My aim is to take up this research direction in order to clarify the relationship between our certainties and diverse kinds of delusions. Specifically, I will shed light on the origin of pedestrian and stark delusions by presenting the concepts of "possibility-blindness" and "uncertainty". To develop both terms, I will take as a reference Ludwig Wittgenstein's later work. 12 There are two reasons as to why section 2 will start by presenting Maher's wellknown model of delusion formation and some criticisms it has received. On the one hand, such presentation will provide an optimal background for describing Wittgenstein's notion of "certainty". On the other hand, I will then be in a position to show that Maher's model and its criticisms revolve around the debate about belief revision, which does not concern certainties because they cannot be modified at will. In this sense, delusions and certainties seem to be independent from each other, yet section 3 will illustrate such relationship by drawing from the distinction Klee made between pedestrian and stark delusions 13 . A provisional definition of pedestrian and stark delusions can be provided by saying that the content of the former may materialize, while the latter is just impossible. Thus, an example of pedestrian delusion can be found in the case of a woman who realized that she was loved by a man who would declare her his love soon although many people were trying to keep them apart 14 : of course, what she says might be true. Conversely, a clear case of stark delusion is that of a woman who repeated time and again in a hospital that she died two weeks ago, around the time of her admission, and wanted to know whether she was already in heaven 15 . Keeping this distinction in mind, I aim to show that pedestrian delusions can often be regarded as a case of "possibility-blindness", a concept which I develop from the notions of aspect-and meaning-blindness that Wittgenstein exposed in his Philosophical Investigations 16 . Subsequently, I will explain why some stark delusions can be considered as a case of "uncertainty", a term which I elaborate by taking as a reference Wittgenstein's On Certainty 17 . Contrary to the prevailing view according to which delusions are beliefs, this will lead me to emphasize the content not of an alleged delusional belief but of an uncertainty or hole opened in our system of certainties after having lost one of them: as Sass pointed out, it has gone almost unnoticed how often delusions entail "not belief in the unreal but disbelief in something that most people take to be true" 18 . Finally, my 10 Eilan, N.: "On understanding schizophrenia", in D. Zahavi (ed.), Exploring the self, Amsterdam, John Benjamins, 2000. 11 Cfr. Bortolotti, L. and Broome, M.R.: "Delusional Beliefs and Reason Giving", Philosophical Psychology, 21(6), 2008, pp. 821-841. 12 I want to emphasize that I developed both concepts by drawing inspiration from Wittgenstein's later work, so that I am the sole responsible for these contributions which should therefore not be regarded as concepts belonging to Wittgenstein's terminology. 13 Klee, R.: "Why Some Delusions Are Necessarily Inexplicable Beliefs", Philosophy, Psychiatry & Psychology, 11(1), 2004, pp. 25-34. 14 Jordan, H.W., Lockert, E.W., Johnson-Warren, M., Cabell, C., Cooke, T., Greer, W. and Howe, G.: "Erotomania revisited: Thirty-four years later", Journal of the National Medical Association, 98(5), 2006, pp. 787-793. 15 McKay, R. and Cipolotti, L.: "Attributional styles in a case of Cotard delusion", Consciousness and Cognition, 16, 2007, pp. 349-359. 16 Wittgenstein, L.: Philosophical Investigations, Oxford, Blackwell, 1986. [Henceforth, "PI"]. proposal -especially regarding the cases of uncertainty -places particular emphasis on the strangeness characteristic of delusions, to the extent that it is no surprise that the delusional subject sometimes undergoes marked emotional changes while hardly being able to express accurately what she feels and even takes for granted.

The apparent distance between delusions and certainties
Delusions have traditionally been considered a result of a thinking disorder, but Maher suggested that many paranoid patients suffer from a perceptual disorder 19 . Specifically, Maher pointed out that this kind of delusions would consist in the hypotheses developed by patients through normal cognitive processes in order to explain abnormal and unexpected perceptual phenomena invested with unusual significance. From this standpoint, the development of such hypotheses seems therefore to be the expected reaction of people who think normally in the presence of unusual experiences. Scientists and paranoid patients are, according to Maher, highly resistant to abandon their theories even in the face of contradictory evidence, although they can accept to replace them by other ones 20 . In fact, Maher added that the best explanation for the delusional subject will be whichever provides a greater feeling of relief of the cognitive dissonance generated by her strange experiences: in other words, the best explanation will be the one that manages to account for all new data which successively contradict the previous theory, so that delusional explanations will usually spread in their comprehensiveness over time.
In this case, it is admitted that people think normally because they continue to share with us countless certainties with no apparent evidence of any sudden or striking discrepancy thereon. By way of example, these people still agree with us on the meaning of basic words, and they also take for granted, among many other things, that they are alive, that physical objects exist, or that their relatives and friends are not automatons. But these certainties are neither ideas which must be explicitly held or defended by the individual nor mental states that may vary depending on multiple factors. Instead, such certainty is a shared "attitude" which is shown or presupposed in whatever we say and do 21 . This means that certainty constitutes a spontaneous attitude that cannot be based on justified grounds, for regardless of how many grounds could be provided for it, none would be "as certain as the very thing they were supposed to be grounds for" 22 . Since certainties make up our "world-picture" or the background against which we distinguish between true and false, they cannot be wrong 23 . Indeed, if an individual started calling a certainty into doubt, we would not conclude she was wrong, for mistakes can only be regarded as such against the background or world-picture provided by our certainties 24 . If someone seriously 19 Maher, B.A.: "Anomalous experience in everyday life: Its significance for psychopathology", The Monist, 82, 1999, pp. 547-570;Maher, B.A.: "Delusions: Contemporary etiological hypotheses", Psychiatric Annals, 22, 1992, pp. 260-268;Maher, B.A.: "Delusional thinking and perceptual disorder", Journal of Individual Psychology, 30(1), 1974, pp. 98-113. 20 Maher, B. claimed to be a centaur, we could not understand what she meant, as we would not know what she "would still allow to be counted as evidence and what not" 25 . This grammatical isolation is what Wittgenstein calls "madness" 26 , which takes place when a claim is not merely wrong but, unlike mistakes, contradicts our certainties, so that there is no room for it in our language-games 27 . As a result, this individual could not be certain of any judgment 28 : in such a case, her whole world-picture would then also be called into doubt, for such system of certainties is not more certain than a certainty within it 29 .
After this brief presentation of Wittgenstein's conception of "certainty", I hope to show that the delusional explanations to which Maher refers are not certainties. To clarify this point, let us start by bringing up the main criticism to Maher's model. Specifically, the objection has been raised that the occurrence of an anomalous experience is not enough to explain how a delusional belief arises. After all, normal healthy subjects do not develop delusional beliefs whenever they have or seem to have unusual experiences. To this should be added that anomalous experience is not usually sufficient to explain the peculiar content of the delusional belief which is allegedly derived from it 30 . In order to solve the deficiencies of Maher's onestage model, some authors have emphasized the necessity of developing a two-stage model in which a second factor causes the anomalous experience to be regarded as veridical 31 . This second factor should consist in a reasoning style or attribution bias that helps to understand the formation and maintenance of delusional beliefs with which deluded subjects are satisfied although other people find such explanations completely bizarre 32 . In this context, delusional beliefs are regarded as a form of persistent and bizarre belief to which the concerned individual holds fast even though she is expected to revise it. Such expectations are therefore unconcerned with 25 OC §231. 26 OC §281. 27 It should be noted that Wittgenstein started by considering certainty as belief in framework propositions because the first passages of On Certainty constituted a response to Moore, who contemplated certainty in propositional terms. But Wittgenstein's account of certainty developed to the extent that he ended up considering it as an instinctive, non-propositional and non-epistemic mode of acting, so that it is also exempt from doubt (cfr. Stroll, A.: Moore and Wittgenstein on Certainty, New York and Oxford, Oxford University Press, 1994). Although this second account came to dominate On Certainty, in this paper I will often refer to the content of certainties -i.e. considering them in propositional terms -because my arguments can then be understood in a much easier way than if I describe attitudes or ways of acting. certainties, for certainties, as Wittgenstein showed, cannot be acquired or revised at will. According to Ariso, certainties cannot be assimilated through a given mental state, by willing to adopt a certainty on a persuader's proposal or by trying to act as if the certainty involved was followed in the finest detail 33 . And last but not least, certainty cannot be acquired through reasoning, as it is ungrounded, ineffable, and is not invalidated even when evidence seems to contradict it.
For the sake of clarity, it is important to make a conceptual distinction here between certainties and beliefs, as Wittgenstein himself warned: "At the foundation of well-founded belief lies belief that is not founded" 34 . Wittgenstein used the term "belief" in On Certainty in two different ways 35 . On the one hand, Wittgenstein referred to a well founded belief because it "is supported by evidence, discovered by playing according to the rules of the language game and thus belongs to the language game", while, on the other hand, the belief that is not founded has no place in our language-games or current linguistic practices because it is ineffable: in fact, it is one of the synonyms Wittgenstein used for "certainty" 36 . To clarify the relationship between beliefs and certainties, it should be noted that certainties are necessary for the existence of belief revision, as such revision can take place only if we have no doubt about aspects as basic as the meaning of the words with which beliefs are expressed. Conversely, certainties are not affected by beliefs and their revisions or variations, as certainties constitute the background through which beliefs make sense, whilst the latter can be seen as mere expressions of some possibilities derived from our certainties and language games. It is therefore obvious that delusional explanations in Maher's model are not certainties, but mere beliefs or ideas. Indeed, belief change takes place when a rational agent adopts a new belief state in order to improve her knowledge 37 . Hence, this belief change involves evaluating and revising beliefs when compelling counter-evidence clearly shows they are false. Of course, this is a complex and, above all, a willful task which requires reasoning skills. That is why Bortolotti wonders regarding subjects who develop delusional beliefs: "why do they accept the belief and maintain it?" 38 In short, two-stage models try to account for a deficit in belief revision, whilst certainties should seemingly remain detached from these models because certainties cannot be revised at will as if they were mere beliefs. Keeping this in mind, delusions and certainties seem to be wholly independent from each other, yet next section will show how the origin of some pedestrian and stark delusions may be explained through certainties. 33 Ariso, J.M.: "Can Certainties Be Acquired at Will? Implications for Children's Assimilation of a World-picture", Journal of Philosophy of Education, 50(4), 2016, pp. 573-586. The fact that I refer to an individual adoptingor losing -a certainty does not mean that it can be reified, as if it were a thing that one merely has. Certainty remains a disposition when we are asleep or unconscious, but all its manifestations are enacted because it takes then the form of "spontaneous acting in the certainty of…" (

The relationship between delusions and certainties
There are significant variations in the commitment to the content of delusions. In many cases, subjects show behavioral, cognitive and affective dispositions incompatible with the content of their delusion 39 , to the extent that they "seem to maintain a critical attitude towards it" 40 , e.g. some patients may even argue and negotiate their delusional claims 41 . But there are also cases in which delusions are held immune from counterevidence and thus constrain the delusional patient's reasoning and interpretation of her experience to such an extent that they seem to have the epistemological status of certainties 42 . This variety in the commitment to the delusional content is also reflected in the distinction that Klee made between pedestrian and stark delusions 43 . As Wittgenstein's conception of "certainty" has already been explained, my previous description of the distinction between pedestrian and stark delusions can now be refined. According to this distinction, that Sass favorably welcomed 44 , pedestrian delusions are regarded as mistakes in Wittgenstein's sense, so that they involve neither denying nor doubting any certainty. Two clear examples of this are delusions of spousal unfaithfulness and of persecution by governmental authorities, as, according to Klee 45 , they do not put any certainty into question: indeed, both things might be true. Conversely, stark delusions involve denying our certainties: a glaring example of this is Cotard syndrome, which is characterized by taking for granted that one is dead, or that one or some part of one`s body does not exist 46 .
Although it is very tempting to consider delusions as certainties, well developed criticisms have been made of this alignment. Thus, Bortolotti and Broome argue that patients affected by heavily circumscribed delusions do not show the behavior which should be expected from someone who were sure of the content of the delusion 47 . Moreover, such content does not fit in but clearly clashes with the rest of the patient's certainties: that is why other people cannot make sense of the  46 Cfr. Berrios, G.E. and Luque, R.: "Cotard's delusion or syndrome?", Comprehensive Psychiatry, 36, 1995, pp. 218-223. delusion due to the changes of meaning relations 48 . Thornton, for his part, raises three objections 49 . First, it is impossible to regard as certain a framework proposition whose content and its relation to other things which are held as certain, known or doubtful cannot be understood; second, framework propositions -through which certainties may be voiced with heuristic purposes -can sometimes be understood as empirical judgments that turn out to be true or false, while delusions are not false but strange or impossible; third, since the structures of thought cannot be described independently of their meaning or content, it is not possible to identify thoughts which are held fast as certainties, so that such certainties could not be identified with delusions either. Nevertheless, Thornton indicates one way to contemplate delusions in terms of certainties. Specifically, he claims that delusions could be seen as a result of or identical to "a breakdown of the pre-epistemic background conditions for a world-picture" 50 , but without regarding specific delusions as particular abnormal certainties. As Thornton does not expand upon this interesting idea, I will develop it by explaining the relationship that certainties may have with pedestrian and stark delusions.

Possibility-blindness in pedestrian delusions
Keeping in mind that the content of pedestrian delusions may be true or false, it seems that they do not affect our certainties at all. By way of example, Maher raises the case of an old man who becomes hard of hearing and is convinced that other people whisper because they are plotting against him 51 . Of course, it is possible that those people are really plotting against the deluded subject, so that the content of the delusion could be either true or false without affecting certainties. The same is true in the case of the woman who is sure that a man will declare her his love despite enemies: if such declaration took place, her world-picture would not change at all. The problem in some of these cases is that the delusional patient seems to have become blind to a specific possibility because he lacks the capacity to admit evidence against the possibility he holds fast to. This blindness is of delusional nature because, according to Parrott, if one accepts to adjust a false conception of epistemic possibility when she is confronted with contradictory evidence, then she is wrong: but if not, she is delusional 52 . I will call "possibility-blindness" this blindness towards any kind of evidence that confirms that a specific possibility has become a reality 53 . 48 Changes of meaning relations take place when the deluded individual expresses his delusion with terms whose meaning does not fit with the meaning or the use we make of such words in our current language-games. To give an example, we cannot understand the individual who states "I am dead".  53 Williams claimed that we all are "alternative-blind" people whose "rule-following does not carry with it any live alternatives" to what we are doing. Thus, this blindness concerns those alternatives that must be overlooked in order to fluently follow the rules of our language-games. Conversely, possibility-blindness concerns an alternative -specifically, a possibility -contained in our language-games. Therefore, while alternativeblindness is, so to say, an implicit part of a rule, possibility-blindness constitutes an incapacity to follow a rule.
To shed more light on possibility-blindness, I will begin by taking as a basis Wittgenstein's remarks about aspect-blindness and meaning-blindness. Wittgenstein was particularly struck by the fact that some people suddenly perceived hitherto unnoticed aspects in pictures like Jastrow's duck-rabbit or the Necker cube although no changes took place in their visual field. In contrast to Gestalt psychologists like Köhler, who ascribed this phenomenon to the way in which the visual object is organized when we perceive it 54 , Wittgenstein argued that what changes in these cases is our attitude to the object, that is, the way we react to it and even the things we can do with it: since we place what we perceive in a different context when noticing an aspect, our perception of it also changes, for "we detect new connections or draw fresh comparisons" 55 . There are people, however, who are unable to notice such aspects, what leads Wittgenstein to talk about "aspect-blindness" 56 : by way of example, an aspect-blind individual will be unable to see a schematic cube as a cube. However, Wittgenstein uses a different term -"meaning-blindness" -to characterize a very similar case, e.g. the case in which a subject lacks the capacity to see the sign "→" as an arrow 57 . Of course, it will be pointless commending him to see it as an arrow: otherwise, it would be out of place to call this a sort of blindness. But if he cannot change the way he sees the sign "→", he will also lack the capacity to see it as pointing not only at a specific moment in time, but also over time. In such a case, the individual will not be able to follow rules related to arrows, so that his ability to use and understand a language will be affected. That is why, according to Nachtomy and Blank, aspect-blindness entails meaning-blindness, which also explains why Wittgenstein uses both terms interchangeably 58 .
Let us see another example of meaning-blindness. Meaning is experienced, for instance, when we laugh at puns. Even though laughing and having the experience of meaning are different things, when someone laughs at puns at the right point we may assume that "he has a feeling for the ambiguity of words" 59 . But when this reaction and other similar ones -like spontaneous utterances − remain absent, it must be concluded that the individual lacks sensitivity towards the meaning of words, and he will thus be regarded as a meaning-blind person. According to Schulte, the term "meaning-blindness" applies only to sophisticated aesthetic nuances 60 , while Zemach points out that such blindness only concerns our capacity to experience qualia or sensations associated with words 61 . Nevertheless, the above-mentioned "→" example suggests that the scope of meaning-blindness is much broader -and more fundamental -than those of refined aesthetic sensitivities or the incapacity to experience qualia, for the meaning-blind individual would also be unable to use signs in the way we do 62 .
It is therefore expected that meaning blind people cannot take part in some language-games, but such cases are not usually identified under the label "meaningblindness" -in Wittgenstein's sense -because this term seems to remain virtually unknown outside philosophical circles 63 . Thus, bearing in mind that we seemingly do not meet meaning-blind individuals in all the huge variety of mankind, we could bring up here the following question Wittgenstein made regarding, among others, meaning-blind people: "Or are there such people among the mental defectives; and it is merely not sufficiently observed which language-games these are capable of and which not?" 64 . Following this hint, the question arises whether spontaneous utterances and reactions of some patients with pedestrian delusions could be reformulated with an expression of the kind of "At this moment I cannot see how X would be possible", where X is a possibility that the individual shared until then with his linguistic community. From a descriptive point of view, it could be said that this individual has become completely alien to the context in which we all place the mentioned possibility. This context includes the linguistic community's agreement regarding the identification of suitable verification procedures without falling into radical skepticism about the validity of gathered evidence; furthermore, such context includes the spontaneous identification of similarities and connections with all other contexts in which verifications are carried out. Hence, possibility-blindness is closely related to aspect-blindness, for the possibility-blind individual can no longer identify similarities between a specific possibility and other ones, so that he does not react to it as if there were really something to be verified. But possibility-blindness is also related to meaning-blindness, as the possibility-blind individual cannot find meaning in a specific possibility, as a result of which he will not be able to understand and take part in a number of language-games.
It should therefore be noted that possibility-blindness does not concern specific proofs but a whole context -in which such proofs become meaningful. That is why the possibility-blind individual neither needs nor can challenge evidence against the possibility he holds fast to, which may explain why some deluded people are seemingly indifferent to such challenges. As he can no longer detect connections or similarities with other verification processes, commands of the kind of "See it as any other verification process!" will not provide him with the suitable context to regain his lost capacity. Since his problem just consists in having become blind or alien to a whole context, thus preventing him from taking part in some languagegames, therapy might be aimed here at a conceptual reconstruction of this context. By way of example, the individual convinced that he is persecuted by governmental authorities may be asked whether this means that, although he is persecuted, it would also be possible that such persecution had never happened. If the answer is negative, he may be told that his position makes no sense: or rather, that we cannot understand 62 Nachtomy, O. and Blank, A.: "Wittgenstein on Aspect Blindness and Meaning Blindness", Iyyun, 64, 2015, pp. 57-76. 63 Cognitive neuropsychologists have been using for some decades the term "word meaning blindness" (cfr. Lambon Ralph, M.A., Sage, K. and Ellis, W.: "Word meaning blindness: A new form of acquired dyslexia", Cognitive Neuropsychology, 13(5), 1996, art. 617), but in a very different sense because it refers to impaired understanding of written words although objects and spoken words can be normally comprehended. 64 Wittgenstein, L.: Remarks on the Philosophy of Psychology, vol. I, Oxford, Blackwell, 1980, §179, see also 182. how he uses the term "persecution", so that he must begin by clarifying this point in order to continue the conversation. His answer to this question -and the ensuing discussion thereon taking as a reference, among others, the indirect assessment of certainties in the clinical setting described by Ariso 65 -might be the first step to understand his incapacity, and, by extension, to make some room for doubt where hitherto there were none.
Once the relationship between possibility-blindness and aspect-as well as meaning-blindness has been shown, I now come to explain what possibilityblindness consists of by bringing up two further terms from Wittgenstein's later work: objective and subjective certainty. To begin with, I will outline the key differences between both concepts. Indeed, objective certainty corresponds to what in this paper I call "certainty" without further specification. Regarding subjective certainty, Wittgenstein describes it as "complete conviction, the total absence of doubt, and thereby we seek to convince other people" 66 . Wittgenstein clarifies in this passage that, unlike subjective certainty, objective certainty is characterized by the logical exclusion of the possibility of mistake; however, it must be clear that Wittgenstein does not refer here to the classical conception of logic, but to the set of rules which shape our language-games 67 . As a result, objective certainty turns out to be "both a personal and a shared certainty" 68 . On the one hand, it is personal or subjective inasmuch as it counts for each one of us as the background underpinning whatever we say and do. On the other hand, such certainty is objective because the logical exclusion of the possibility of mistake thereon is established not subjectively or by ensuring that one is not making a mistake, but in the grammatical rules we share by taking part in language-games.
Bearing in mind the distinction between objective and subjective certainty, it could be argued that possibility-blindness might be contemplated as the acquisition of the objective certainty "At this moment I see X as impossible": but it should not be forgotten that this proposition does not express any certainty because it does not constitute an assumption shared by the linguistic community. Stated otherwise, our language-games do not indicate how it can be objectively established that X is impossible: instead, X is one of the countless possibilities contained in our languagegames, and, by extension, in our world-picture. Therefore, as the very expression "At this moment I see…" suggests, it appears to be a subjective certainty. Nevertheless, the following example illustrates that subjective certainty does not constitute possibility-blindness, but only part of it.
Admittedly, many mentally healthy people appear to be possibility-blind with some of their beliefs, to the extent that searching for evidence and engaging in debate with themselves or others on those issues becomes pointless. It would be a mistake, however, to confuse possibility-blindness with mere stubbornness. Indeed, there are many people who seem unable to accept a concrete possibility, but they actually know what facts they would accept as evidence in favor of it, in addition to which they are aware that those facts might take place. The problem is that these stubborn people cling so firmly to their desire or conviction that such facts will not happen, that they appear to be possibility-blind. These stubborn people are subjectively certain that the possibility X cannot materialize, but regardless of the irony or hostility with which they seem to deny X, they still share the objective certainty that X can materialize. Proof of this is the fact that if the possibility materializes, and regardless of how they handle the initial surprise, they will be able to accept contrary evidence and to attribute meaning to that situation.
In principle, it may sound strange that many language-games enable us to show subjective certainty against an objective certainty, but it should be noted that such language-games leave room for this provided that we keep sharing the objective certainty. For instance, someone may express with derision or condescension his subjective certainty that it is virtually impossible for a woman to be loved by a specific man, while admitting the extremely slight possibility that such a thing may happen. When objective certainty is lost, however, it is no longer a case of stubbornness but of possibility-blindness. Of course, possibility-blind people are also subjectively certain that X cannot materialize. Indeed, it is expected that subjective certainty is even more acute in the case of possibility-blindness because it then becomes impervious to evidence and reasoning: after all, Wittgenstein himself presents it as "complete conviction, the total absence of doubt" 69 . In my view, the fact that subjective certainty is more intense in possibility-blindness than in stubbornness reveals the difference between them: while the stubborn individual keeps admitting the possibility X, albeit reluctantly, the possibility-blind person, as the name already implies, has become completely blind or alien to it irrespective of his will. Before, he could distinguish and accept those proofs or circumstances that should lead him to admit he was wrong thereon, but he no longer even attempts to refute any proof because the very possibility that makes these proofs meaningful has become inconceivable for him. Thus, he cannot see how his stance can and should be overturned. Maybe the stubborn individual does not want to accept and work through the consequences of contrary evidence, but the possibility-blind one simply cannot do it. Hence, it comes as no surprise that his subjective certainty is even more acute than the stubborn person's one; however, what is relevant here is not the degree of subjective certainty but whether he keeps sharing the objective certainty that the possibility X can materialize.
Let us return to four previous examples of pedestrian delusions in order to illustrate the difference between possibility-blindness and stubbornness. A woman who is sure that a man loves her and will declare her his love soon despite enemies, an old man convinced that other people plot against him, a husband who believes that his wife is unfaithful, and an individual convinced that he is persecuted by governmental authorities could take any compelling evidence of being wrong, glaring as it may be, as a mishandling of evidence or, worse still, as a new act of conspiracy. These stubborn individuals could try to deny or distort evidence, but that would also prove they had previously admitted such evidence as valid; in fact, the very attempt to deny evidence would reveal that the individual had given meaning to the situation, as deep inside he never failed to admit that the possibility to which he seemed to be blind could materialize. Conversely, the possibility-blind subject will 69 OC §194. be unable to understand any evidence for a specific possibility, to the extent that he cannot attribute meaning to the situations arising from the materialization of such possibility. He will therefore not think that other people are manipulating evidence to try to convince him thereon, as the possibility they are considering does not exist for him: instead, he will find it absurd that they insist on presenting evidence where -due to his possibility-blindness -he can identify no room for any kind of proof.
Unlike the alleged delusional certainties, it seems that we should easily understand the loss of a certainty like "It is possible that X is the case" because the patient shared it with us and we are quite well acquainted with it, to the extent that we have a clear idea of which reactions to different types of evidence related to this certainty could be expected. Yet even though this loss or incapacity lasted over time, we could not understand the patient affected by it. This idea seems counterintuitive, for the subject does not reject the possibilities that X is either true or false, but clings on to one of them. In this case, however, there is no room even for a partial understanding -or, so to speak, at fifty per cent -because the admission of supporting evidence makes sense only if one is also able to admit contradictory evidence. This means that plot, deceit and persecution will not be true or false for the patient with possibilityblindness in view of available evidence, but paradoxically, they will be events that have happened even though they have not really occurred. In short, such blindness affects certainties because the individual no longer shows the certainty "It is possible that X is the case": while blindness persists, the patient will not share this certainty, and, as is well known, blindness can be either temporary or chronic. In any case, ephemeral episodes of possibility-blindness should not be discarded as irrelevant, for they can be of great help to detect predelusional states.

Uncertainty in stark delusions
The loss of a certainty is not only imaginable: indeed, it sometimes occurs 70 . At first glance, it might be thought that some certainties are so basic that they cannot be affected or lost at any time, yet Le Roy Finch claims that there is "no certainty which can remain unaffected through every eventuality, including drugs, madness, dreams, delusions, and illuminations" 71 . Likewise, Ariso points out that man cannot avoid "the possibility of losing any certainty at any moment and under any circumstance", but in addition, he argues that it is not up to us to regain a lost certainty 72 . This is an important point, because if certainties cannot be acquired at will 73 , when one of them is lost, it is not possible to replace it by another one, but neither can it be regained willfully.
In this article I will call "uncertainty" the scenario generated when losing a certainty. In such cases, I would add, the subject is sure of having lost a certainty, or rather, the patient feels she has lost confidence regarding some basic aspect of her world-picture. Since she finds this situation distressing and cannot understand what has happened, she looks for an explanation that helps relieve cognitive dissonance. As the patient does not usually think that she could be suffering from a − maybe transient − disorder, she tries to find an account of the situation which is as clear and convincing as possible. This account is a mere idea developed with the aim of plugging the hole generated by the loss of a certainty. However, it is highly problematic to use an idea as a substitute for a certainty because certainties must already have an extraordinarily large number of connections between them: it is not in vain that our certainties make up our world-picture and are reflected so spontaneously in what we say and do that we are not even aware of them. Instead, the idea appears as something that the individual furnishes and maintains, so that she often must pause to think how to adjust it to the facts. Indeed, Bortolotti and Broome noted that patients with Capgras often admit that "the content of their delusion is implausible, sometimes even unbelievable", while they do not find the content of their certainties unbelievable or implausible 74 . In this vein, it seems reasonable to assume that some delusional subjects can find themselves in an odd situation: on the one hand, they are sure of their uncertainty, but on the other hand, they have reservations about the idea with which they try to account for such uncertainty. If they are unable to distinguish between both things, it should come as no surprise that they end up confusing them.
The explanation I have just offered is compatible with evidence gathered on some patients with Capgras and Cotard syndrome. Thus, Bayne and Pacherie remarked that Capgras patients not only fail to experience the normal feeling of familiarity when seeing a specific person, but also have an annoying feeling of estrangement; moreover, these patients are unable to specify what has changed in their experience 75 . In this regard, Wittgenstein notes that if he raised doubts regarding the identity of an old friend opposite him, such "a doubt would seem to drag everything with it and plunge it into chaos" 76 . This doubt would have a devastating effect because it would constitute the loss of a certainty, that is, what I have called "uncertainty". The Capgras patient has lost the confidence with which she always recognized a loved one, but as she cannot stand cognitive dissonance and needs to make some sense of her experience, she develops an idea that can hardly be adjusted to or accommodated in her world-picture 77 . As can be appreciated in the following quote, something similar occurs with Cotard patients: We asked her during the period in which she claimed to be dead whether she could feel her heart beat, whether she could feel hot or cold and whether she could feel whether her 74 Bortolotti, L. and Broome, M.R.: "Delusional Beliefs and Reason Giving", Philosophical Psychology, 21(6), 2008, pp. 821-841, p. 832. Capgras delusion, also known as "impostor syndrome", is characterized because the patient is convinced that an important person in her life, usually a relative, has been replaced by an impostor. These patients may recognize that the alleged impostor looks exactly like the original person, despite which they think that they are able to discover the deception. For instance, a woman could not recognize the man who was driving the family car as her husband: she admitted that he looked very much like her husband, but she added that he was just a bit fatter (cfr. Sims, A.: Symptoms in the Mind, Saunders, Elsevier, 2003). 75 Bayne, T. and Pacherie, E.: "Bottom-Up or Top-Down: Campbell's Rationalist Account of Monothematic Delusions", Philosophy, Psychiatry, and Psychology, 11(1), 2004, pp. 1-11. 76 OC §613. bladder was full. JK said that since she had such feelings even though she was dead they clearly did not represent evidence that she was alive. 78 Regarding this case, Bayne and Pacherie made an interesting comment: JK is obviously not indifferent to the tension between her delusional state and her background beliefs (which, incidentally, suggests that she has not lost her grip on the meanings of the words she uses), but rather than retain her background beliefs concerning the marks of being alive, she retains the delusion that she is dead. So in this respect her delusion functions as a framework belief. 79 Indeed, JK fails to explain how her certainty of being dead may fit with the tokens of being alive: she simply maintains that such tokens do not constitute valid evidence of being alive because she was dead. Nevertheless, certainties are ungrounded, so that they do not require evidence that justifies them. Stated otherwise, there is no such thing as the accommodation of a certainty because certainties are such when they are already accommodated. Certainties provide the background from which we accommodate beliefs, give reasons, and take part in any other language-game. But more importantly, Bayne and Pacherie emphasize the tension that JK perceives between her delusional state and her world-picture or system of certainties. In that connection, Bayne and Pacherie wonder later why patients like JK are puzzled by the thought that other people might share their belief, if it really is a certainty 80 . In my opinion, and despite of the sureness shown by JK when expressing the content of her delusion, it might be of interest to distinguish between her sureness that something totally unusual happened to her and the account she offers of such experience. To shed light on this issue, I will reformulate not the certainty but the uncertainty that might be found in the origin of some Cotard and Capgras delusions.
Let us suppose that someone, for whatever cause, has lost a certainty some time ago. Despite appearances, this process would be far simpler than the development of an alleged delusional certainty. If it really were a certainty, it should have already been accommodated within the rest of certainties, which requires time as well as very numerous and deep adjustments. In contrast, the loss of a certainty simply involves uncertainty, which does not request any adjustment and may even happen suddenly. Let us thus imagine that a Cotard patient − like the woman who was sure of having died two weeks ago, around the time of her admission − instead of assimilating the certainty "I am dead", has lost the certainty "I am alive". At first glance, these are two different ways of saying the same thing, as it seems logical to conclude that one is dead if one is not alive. Yet appearances may be deceptive. "I am not alive" is an expression of uncertainty, which, as such, cannot be accommodated within the patient's world-picture. Although she is aware that there are tokens of being alive, she does not feel alive. We can thus go a step further in the reformulation of the uncertainty by expressing it as "I do not feel alive". Faced with such a distressing uncertainty, it is not surprising that the patient expresses herself not only in positive terms but also in the simplest way: "I am dead". That is the idea with which the patient attempts to account for the hole of uncertainty, though, paradoxically, the idea used to express such uncertainty must strike her inasmuch as it is not wellintegrated in her world-picture.
Seemingly, the uncertainty "I do not feel alive" would be utterly incomprehensible because it has no room in what Wittgenstein called our "form of life" 81 , but maybe in something as strange for us as an alleged "form of death". Leaving such a bizarre concept aside, the important thing is to analyze to which extent the mentioned uncertainty can have room in our form of life. After all, the uncertainty in question is not "I am not alive" but "I do not feel alive", which is fully compatible with being alive and having a disorder in which one faces a strange experience that one interprets as best one can. Of course, we cannot understand what is literally meant when a patient says that she does not feel alive; but if we take the proposition "I do not feel alive" as a peculiar way of expressing things that are so difficult to describe as lack of affective response 82 , depersonalization-derealization 83 or low sense of agency 84 , among others, then this expression can make sense within our form of life. According to Klee, clinicians usually have no problem with identifying the content of stark delusions 85 , yet it seems reasonable to think that there may be cases when the origin of a delusion lies in an uncertainty which has not been identified, or even correctly expressed, by either the clinician or the patient. Wittgenstein refers always to certainties whose content -or formulation through a framework propositionis absolutely clear, but Ortega warns that a man or a whole civilization cannot be known until it is clarified which certainties really make up their corresponding world-pictures 86 . To this I would like to add that some certainties -and, by extension, also the uncertainties resulting from their loss − may be very difficult to identify because they concern aspects and feelings which we are not aware of until they are missed, which very rarely happens. A clear example of this is the "personalization" and "realization" that we must somehow or other continuously experience if it makes sense to talk of a "depersonalization-derealization disorder". If such certainties exist, it should come as no surprise that the patient finds it very difficult to express their loss -also due to the distressing situation she is experiencing -and that she describes her uncertainty in the simplest and most resounding way. 81 PI §19, 23.

82
A similar reformulation could be made regarding some Capgras cases. Instead of considering the alleged delusional certainty "This person is not my relative but an impostor", it could be interesting to start taking as a reference the uncertainty "He is not my relative". The problem is that this uncertainty puzzles the patient, who does not regard it as a psychological disorder: that is why she concludes "He is an impostor". But if the uncertainty is reformulated as "I cannot recognize my relative when I look at this person", this would not exclude the possibility that the person opposite her is the relative in question, as this peculiar situation might be due to a disorder. If the patient were invited to contemplate her case in this way, she might acknowledge then that she understands it more clearly, which could make that situation much more bearable for her. It is true that cognitive biases − like the jumping to conclusions bias, which leads to hasty decision-making based on limited evidence -may play an important role in these cases; yet empirical findings make it advisable to treat such delusions by applying reasoning-focused interventions 87 . Specifically, cognitive restructuring may help delusional patients to verify that their interpretations of reality are inaccurate, but also to improve their cognitive strategies to deal with delusions 88 : in this vein, Ariso has shown that cognitive restructuring may become more effective in detecting and dismantling disturbing thoughts by using Augmented Reality 89 .

Conclusion
The conceptual contributions I have made in this article may appear identical; nevertheless, there is a clear difference between them. Thus, possibility-blindness takes place when there are two possibilities regarding a proposition -which may be either true or false -and someone is unable to admit one of those possibilities by not considering any kind of contradictory evidence as valid. Although the individual rules out one possibility in an apparently arbitrary way, he may seemingly be right because the only possibility that he was able to admit could be eventually materialized. Conversely, uncertainty occurs when a certainty which makes up our world-picture is lost, so that the ability to admit evidence either for or against a given alternative is not lost: instead, the subject misses a basic assumption for which there are no alternatives within our world-picture. At first sight, the alternative to "I am not alive" is "I am alive", yet if we consider our world-picture, they are not alternatives: while the former is a piece of nonsense, the latter is a certainty.
Delusion was not regarded in this article as a thinking disorder because the patient reasons as best one can in such circumstances. Even though the possibilityblind patient is able to admit evidence solely for the option he holds fast to, he is expected to understand that this acceptance makes sense only if he is also willing to admit contradictory evidence: at the very least, he should acknowledge that the rest of people -and, above all, he himself heretofore -accept it without major problems. In contrast, uncertainty entails losing a certainty that can be very difficult to identify: this causes a drastic change in his world-picture that the patient interprets in the simplest way, though it could be far easier for him to develop a more critical attitude towards his delusion -to the extent that it might even disappear totally or partiallyif he were assisted in realizing that he had wrongly interpreted the loss of a certainty.
Possibility-blindness and uncertainty constitute individual deviations of the very system of certainties or shared instinctive attitudes that make it possible to take part in language-games and preserve rationality. As Berrios and Fuentenebro pointed out, the term delirio, which means "delusion" in Spanish, Italian and Portuguese, comes from the Latin delirare, that is divided into de -out − and lirare -to plough -which, in turn, is close to lira -furrow: hence, delirare means "to get out of the furrow, not to plough straight" 90 . Indeed, to get out of the furrow of one's world-picture may create in the deluded patient an extraordinary sense of vulnerability. Sass warned that psychiatrists and clinical psychologists have focused almost exclusively on etiology, thus dismissing particular forms of experience and action as "inferior versions of the norm" 91 . In this vein, Drury remembers that Wittgenstein told once that, if he were suffering from delusions, what he should fear at most is a common-sense attitude from the psychiatrist, that is, that the clinician seemed to take such a state as a matter of course 92 . From Drury's standpoint, Wittgenstein meant that clinicians should let their deluded patients see that they understand that it is "a state of affliction which is not comparable to any bodily pain however severe". In other words, particular attention should be given to the strangeness characteristic of many delusions, to the extent that it could be expected that the patient experiences remarkable affective changes, above all fear 93 , and that he sometimes is unable to transmit accurately what he feels as well as even what he is certain of.