In this thesis I discuss the problems associated with the epistemological task of arriving at basic logical knowledge. This is knowledge that the primitive rules of inference we use in deductive reasoning are correct. Knowledge of correctness, like all knowledge, is available to us either as the product of inference, or it is available non-inferentially. Success in the campaign to justify the correctness of these rules is mired by opposing views on how to do this properly. Inferential justifications of rules of inference, which are based on reasons, lead to regressive or circular results. Non-inferential justifications, based on something other than reasons, at first do not seem to fare any better: without a basis for these justifications, they appear arbitrary and unfounded. The works of Boghossian and Dummett who argue for an inferentialist approach, and Hale who supports non-inferentialism are carefully examined in this thesis. I conclude by finding superiority in Hale's suggestion that a particular set of basic logical constants are indispensable to deductive reasoning. I suggest that we endorse a principle which states that rules are not premises, and are therefore to be excluded from expression as statements in a deductive argument. I argue that the quality of being indispensable is sufficient for a basic rule of deduction to be countenanced as default-justified, and therefore need not be expressed in argument. By a rule's evading expression in argument, it avoids circular reasoning in deductive arguments about its own correctness. Another important outcome that emerges from my research is the finding that non-inferential knowledge is ontologically prior to the inferential sort. This is because plausible inferential knowledge of basic logical constants shall always be justified by circular reasoning that already assumes the correctness of the rule to be vindicated. This initial assumption is tantamount to non-inferential knowledge, and therefore this latter is more primitive-in fact the only primitive-species of basic logical knowledge.

In this thesis I discuss the problems associated with the epistemological task of arriving at basic logical knowledge. This is knowledge that the primitive rules of inference we use in deductive reasoning are correct. Knowledge of correctness, like all knowledge, is available to us either as the product of inference, or it is available non-inferentially. Success in the campaign to justify the correctness of these rules is mired by opposing views on how to do this properly. Inferential justifications of rules of inference, which are based on reasons, lead to regressive or circular results. Non-inferential justifications, based on something other than reasons, at first do not seem to fare any better: without a basis for these justifications, they appear arbitrary and unfounded. The works of Boghossian and Dummett who argue for an inferentialist approach, and Hale who supports non-inferentialism are carefully examined in this thesis. I conclude by finding superiority in Hale's suggestion that a particular set of basic logical constants are indispensable to deductive reasoning. I suggest that we endorse a principle which states that rules are not premises, and are therefore to be excluded from expression as statements in a deductive argument. I argue that the quality of being indispensable is sufficient for a basic rule of deduction to be countenanced as default-justified, and therefore need not be expressed in argument. By a rule's evading expression in argument, it avoids circular reasoning in deductive arguments about its own correctness. Another important outcome that emerges from my research is the finding that non-inferential knowledge is ontologically prior to the inferential sort. This is because plausible inferential knowledge of basic logical constants shall always be justified by circular reasoning that already assumes the correctness of the rule to be vindicated. This initial assumption is tantamount to non-inferential knowledge, and therefore this latter is more primitive-in fact the only primitive-species of basic logical knowledge.

Die Dissertation behandelt die Zusammenhänge zwischen den beiden einflußreichsten neueren Theorien über die Logik von Konditionalsätzen: der auf die Mögliche-Welten-Semantik zurückgreifenden, primär für konjunktivische Konditionalsätze entwickelten Theorie von David Lewis und derjenigen von Ernest Adams, die primär für indikativische konzipiert wurde und in der Tradition des Bayesianismus steht. Bei dem Versuch, beide Theorien auf den indikativischen Bereich anzuwenden, erwiesen sich die Lewisschen Trivialitätstheoreme als schwerwiegendes Problem. Die wichtigsten der in der Literatur vorgeschlagenen Lösungsansätze (z.B. diejenigen von V. McGee, B. v. Fraassen und F. Jackson) werden in der Dissertation ausführlich erörtert und als unbefriedigend zurückgewiesen. In diesem Kontext findet auch eine Diskussion von McGees Kritik an der generellen Gültigkeit des Modus-ponens-Prinzips statt. Anschließend wird dargelegt, warum Adams´ Versuch, seine Analyse auf konjunktivische Konditionalsätze anzuwenden, scheitert und daß aus sehr ähnlichen Gründen die kausale Entscheidungstheorie von A. Gibbard und W. L. Harper in ihrer gegenwärtigen Form zu Widersprüchen führt. Der Schlußteil der Arbeit zeigt, daß sich die Zuständigkeiten der beiden Theorien nur auf der Grundlage einer neuen Klassifikation angemessen bestimmen lassen. Die übliche Indikativ/Konjunktiv-Dichotomie muß durch eine auf kontextuelle Kriterien rekurrierende Unterscheidung im Bereich der indikativischen Konditionalsätze in eine Trichotomie überführt werden. Es wird nachgewiesen, daß unter weithin akzeptierten Voraussetzungen zu einer der drei Teilklassen nur solche Sätze gehören, die nicht im selben Sinne wie andere Aussagesätze wahr oder falsch sein können.

This thesis is essentially a portfolio of four disjoint yet thematically related articles that deal with some semantic aspect or another of natural language conditionals. The thesis opens with a brief introductory chapter that offers a short yet opinionated historical overview and a theoretical background of several important semantic issues of conditionals. The second chapter then deals with the issue of truth values and conditions of indicative conditionals. So-called Gibbard Phenomenon cases have been used to argue that indicative conditionals construed in terms of the Ramsey Test cannot have truth values. Since that conclusion is somewhat incredible, several alternative options are explored. Finally, a contextualised revision of the Ramsey Test is offered which successfully avoids the threats of the Gibbard Phenomenon. The third chapter deals with the question of where to draw the so-called indicative/ subjunctive line. Natural language conditionals are commonly believed to be of two semantically distinct types: indicative and subjunctive. Although this distinction is central to many semantic analyses of natural conditionals, there seems to be no consensus on the details of its nature. While trying to uncover the grounds for the distinction, we will argue our way through several plausible proposals found in the literature. Upon discovering that none of these proposals seem entirely suited, we will reconsider our position and make several helpful observations into the nature of conditional sentences. And finally, in light of our observations, we shall propose and argue for plausible grounds for the indicative/subjunctive distinction.distinction. The fourth chapter offers semantics for modal and amodal natural language conditionals based on the distinction proposed in the previous chapter. First, the nature of modal and amodal suppositions will be explored. Armed with an analysis of modal and amodal suppositions, the corresponding conditionals will be examined further. Consequently, the syntax of conditionals in English will be uncovered for the purpose of providing input for our semantics. And finally, compositional semantics in generative grammar will be offered for modal and amodal conditionals. The fifth and final chapter defends Modus Ponens from alleged counterexamples. In particular, the chapter offers a solution to McGee’s infamous counterexamples. First, several solutions offered to the counterexamples hitherto are all argued to be inadequate. After a couple of observations on the counterexamples’ nature, a solution is offered and demonstrated. the solution suggests that the semantics of embedded natural language conditionals is more sophisticated than their surface syntax indicates. The heart of the solution is a translation function from the surface form of natural language conditionals to their logical form. Finally, the thesis ends with a conclusion that briefly summarises the main conclusions drawn in its preceding chapters.