Logic, Normativity, and the A Priori Theodora Achourioti Abstract: The aim of this thesis is to explore how an informed and revised notion of normativity reclaims the a priori character of logic. Chapter 2 explores the notion of fallacy and draws upon experimental results to show that there is a gap between traditional standards of rationality and how people actually reason. Furthermore, it argues that what people do in these experiments is nonetheless reasonable. This leads to a redefinition of the notion of fallacy. In the final section, the chapter introduces an idea that is fundamental to the thesis, namely that in reasoning one must go 'beyond the information given'. In an attempt to add further precision to the concept of rationality, Chapter 3 distinguishes two kinds of normativity: external normativity, which relies on norms supposed to be already given, contrasted with internal normativity, which considers norms that are in a sense inherent in cognitive tasks. This topic is further developed in chapter 4, where internal normativity is explained using the concept of constitutive norms as defined by Kant in the first Critique. Constitutive norms are tied up with a fundamental feature of cognition, namely that a process of synthesis is necessary to produce coherent cognitions at all. This is the topic of Chapter 5. In Chapter 6, logic again comes to the fore. It is argued that logic actually embodies two kinds of norms, constitutive and regulative norms. The first attempt to make this idea more precise is via the proof-theoretic semantics pioneered by Dummett and Prawitz. Very roughly speaking, one may identify the introduction rules in natural deduction system with the constitutive norms, whereas the elimination rules fall under the rubric of the regulative norms. In the end, these ideas are found wanting, however, and the next chapter proposes a much more general definition. In Chapter 8, the focus is on reasoning tasks. It is shown that, as a result of the preceding considerations, the relation between competence and performance in these tasks is vastly more complex than entertained in current psychology of reasoning. Finally, Chapter 9 returns to the original question: in what sense is logic a priori?