Doctoral Dissertation: Fragmented Justification

This doctoral dissertation develops a novel account of fragmented epistemic justification. It departs from and expands on the literature on fragmented accounts of belief, and develops a theory where not belief, but the justification of belief, is fragmented. This account is novel, and an addition to the already existing literature on fragmented accounts of belief. It will also shed light on and help to develop answers to some underdiscussed and unsolved questions in the existing literature on fragmentation, such as questions about the rationality of fragmentation. In a nutshell, what it means for justification to be fragmented will be that some piece of evidence might justify a certain proposition relative to some mental fragment, whereas that same piece of evidence might not justify that same proposition relative to a different mental fragment. The epistemic and non-epistemic circumstances, such as differences in accessible information, or different perspectives, focus, or practical goals etc., of the agent can vary across fragments, which is why these circumstances will be the parameters distinguishing fragments from each other. What exactly this means will become clear throughout this dissertation. For the first qualitative part of the dissertation, justification will be modelled to be a non-monotonic justification relation that holds between pieces of evidence and the propositions they justify, which will be indexed to fragments. Fragments, here, will be modelled by using total plausibility pre-orders over possible worlds. Later on, within a quantitative account of fragmented justification, there will be a variety of ways to spell out the concept of justification. Here, fragments will be modelled by using (subjective) probability functions or credence functions. After an introductory chapter, there will be a chapter focusing on an overview over relevant literature that is being discussed or worked with in this dissertation. Then, chapter 3 presents a skeleton of a qualitative (non-probabilistic) account of fragmented justification and shows how this account is able to provide a novel and attractive solution to the preface paradox (Makinson, 1965), one of the central paradoxes of epistemology. Then, chapter 4 develops a more full fledged account of qualitative fragmented justification, using this time not the preface paradox but a scenario from climate science as a motivating example for the account. Here, a scientific expert about climate science seems to be justified in believing an overall inconsistent set of propositions. The chapter explains how the toolkit of orthodox epistemology is limited in dealing with situations like this, and argues that fragmentation is a more appropriate strategy than existing approaches to deal with (seemingly rational) inconsistent doxastic states. The chapter provides a formalisation of this example, as well as a number of justifying reasons for why fragmentation can be rational. It, also, develops some precautionary norms of fragmentation. It concludes by explaining how fragmented justification relates to belief, and argues that fragmented justification provides a novel rationality argument for accounts of fragmented belief, and, furthermore, how one should go about de-fragmenting in light of practical rationality. Chapters 5 and 6 turn to a probabilistic or quantitative account of fragmented justification -- fragmented Bayesianism. Chapter 5 presents a very general version of fragmented Bayesianism, much more general than the existing accounts of fragmented Bayesianism that already exist. The basic idea is that the doxastic state of an agent will be represented not by one credence function, but by a set of credence functions, corresponding to different fragments. The focal point of this chapter is a list of parameters, such as background knowledge, algebra, con