Abstract In this research report, the author defends Peter van Inwagen’s modal skepticism. Van Inwagen accepts that we have much basic, everyday modal knowledge, but denies that we have the capacity to justify philosophically interesting modal claims that are far removed from this basic knowledge. The author also defends the argument by means of which van Inwagen supports his modal skepticism. Van Inwagen argues that Stephen Yablo’s recent and influential account of the relationship between conceivability and possibility supports his skeptical claims. The author’s defence involves a creative interpretation and development of Yablo’s account, which results in a recursive account of modal epistemology, what the author calls the “safe explanation” model of modal epistemology. The defence of van Inwagen’s argument also involves a rebuttal to objections offered to van Inwagen by Geirrson and Sosa.

<p>This study deals with the thesis that conceivability implies possibility. Confronted with alleged counterexamples to this thesis, some philosophers have turned to what may be called “idealized” or “more demanding” notions of conceivability. I argue that in turning to such notions, they have made the thesis useless to limited beings like us for attaining modal knowledge. However, in refusing to identify conceivability with demanding or idealized notions, we cannot maintain that conceivability always implies possibility. Essentially, there are two ways to proceed: to view conceivability as a mere guide to possibility, or to argue that the conceivability thesis is a local truth, i.e., a truth with respect to a certain class of statements. I defend the latter alternative. This class of statements employs concepts with respect to which doubt concerning the conceivability thesis is to be regarded as general skepticism, not as skepticism relating to the conceivability thesis itself.</p><p>I proceed by outlining an interpretation of strict possibility—i.e., the kind of possibility that I take the conceivability thesis to be about—according to which modal truths depend essentially on conceptual relations, as opposed to obtaining purely in virtue of properties of things themselves. Given this account, on which both ideal conceivability and strict possibility have a conceptual ground, I argue that these notions are not only coextensional but relate to one and the same property of statements. I further argue that the impossible is unimaginable, but that it is conceivable in the sense that one can misdescribe the contents of imagination.</p>

This study deals with the thesis that conceivability implies possibility. Confronted with alleged counterexamples to this thesis, some philosophers have turned to what may be called “idealized” or “more demanding” notions of conceivability. I argue that in turning to such notions, they have made the thesis useless to limited beings like us for attaining modal knowledge. However, in refusing to identify conceivability with demanding or idealized notions, we cannot maintain that conceivability always implies possibility. Essentially, there are two ways to proceed: to view conceivability as a mere guide to possibility, or to argue that the conceivability thesis is a local truth, i.e., a truth with respect to a certain class of statements. I defend the latter alternative. This class of statements employs concepts with respect to which doubt concerning the conceivability thesis is to be regarded as general skepticism, not as skepticism relating to the conceivability thesis itself. I proceed by outlining an interpretation of strict possibility—i.e., the kind of possibility that I take the conceivability thesis to be about—according to which modal truths depend essentially on conceptual relations, as opposed to obtaining purely in virtue of properties of things themselves. Given this account, on which both ideal conceivability and strict possibility have a conceptual ground, I argue that these notions are not only coextensional but relate to one and the same property of statements. I further argue that the impossible is unimaginable, but that it is conceivable in the sense that one can misdescribe the contents of imagination.

Hur har vi kunskap om vad som är möjligt? Enligt vad som kan betraktas som det traditionella svaret till den frågan, har vi kunskap om modalitet via föreställningsbarhet. Vi föreställer oss ting och tar sedan detta som bevis för möjlighet. Denna uppsats kommer att undersöka tre invändningar till detta svar angående hur vi har kunskap om möjlighet. Vi kommer sedan att överväga Williamsons förmodan: att vår kognitiva kapacitet för att hantera kontrafaktiska konditionaler bär med sig den kognitiva kapaciteten för oss att även hantera metafysisk modalitet (2007, 136), och undersöka om denna förmodan undviker dessa invändningar. Det kommer här att argumenteras att Williamson’s förmodan undviker två av invändningarna och att den inte tycks kunna svara på den sista invändningen. Det kommer även att argumenteras att en invändning mot Williamson’s förmodan ser ut att vara särskilt problematisk, och att det inte är klart att Williamson’s förmodan är i någon bättre position än den negativa föreställningsbarhets vyn. / How do we have knowledge of what is possible? On what could be considered as the traditional response to this question, we have knowledge of modality by conceivability. We conceive of things and on the basis take this as evidence for possibility. This thesis will consider three objections to this response of how we have knowledge of possibility. We will then consider Williamson’s conjecture: that our cognitive capacity to handle counterfactual conditionals carries the cognitive capacity for us to also handle metaphysical modality (2007, 136), and see if this conjecture avoids these objections. It will be argued that Williamson’s conjecture avoids two of the objections and that it does not seem to have a response to the last objection. It will also be argued that one objection to Williamson’s conjecture seems particularly problematic, and that it is not so clear that Williamson’s conjecture is any better off than the negative conceivability view.

Les arguments de concevabilité sont des arguments philosophiques reposant sur le principe selon lequel tout ce qui est concevable est possible. Cette thèse se propose d'évaluer à un niveau général cette forme d'argumentation en s'appuyant sur des exemples historiques et contemporains. les arguments de concevabilité, quelle que soit la position philosophique qu'ils visent à défendre, soulèvent en effet des difficultés qui leur sont communes et ont trait principalement (i) à la définition de la notion de possibilitée, (ii) à la définition de la notion de concevabilité, et (iii) à la légitimité de l'inférence allant de l'une à l'autre. Le travail consiste d'abord (chapitres 1-3) à construire la catégorie que constituent les arguments de concevabilité en spécifiant notamment le genre de thèses philosophiques qu'ils peuvent chercher à établir. Une fois précisés les objectifs que les arguments de concevabilité peuvent viser, il s'engage (chapitres 4-8) dans l'examen de savoir si les ressources fournies par Ia concevabilité et l'inférence menant du concevable vers le possible suffisent à les atteindre. Pour ce faire, le travail propose une analyse détaillée des différentes formes de possibilité (chapitres 4-5) et de concevabilité (chapitres 6-8) impliquées dans ces arguments. II aboutit à une position dite sceptique modérée au sujet de la validité de cette forme d'argumentation, sur la base de la démonstration que, pour les thèses philosophiques qui nécessitent l'etablissement d'une possibilité métaphysique, la concevabilitée s'avère être un guide insuffisamment fiable, quelle que soit la manière dont on comprend la concevabilité. Mais il défend aussi l'idée que le fait que les arguments de concevabilité ne soient pas toujours concluants n'implique pas qu'ils sont depourvus d'utilité argumentative: car ils nous obligent à clarifier les implications modales de nos conceptions philosophiques et la manière dont nous pouvons raisonner au sujet de ces implications. Cette conception des arguments de concevabilité est appliquée pour finir à la clarification d'un chapitre essentiel de la philosophie de la cognition contemporaine relatif à la possibilité de fournir une explication naturaliste (physicaliste) de la conscience phénoménale, et ou un argument de concevabilité qui a fait couler beaucoup d'encre, dit argument des zombis, joue un rôle essentiel. / Conceivability arguments are philosophical arguments which rely crucially on the principle according to which conceivability entails possibility. This dissertation provides an analysis and a critical assessment of this kind of argumentative strategy, on the basis of contemporary and historical examples. Various possible explanations of the notion of conceivability are considered and it is argued that the inference from conceivability to possibility does not enable conceivability arguments to reach all their intended conclusions, especially those pertaining to substantial metaphysical issues.