How can an experiment which occurs only in thought lead to new and accurate conclusions about the world beyond thought? What makes thought experiments relevant to the domains they are designed to explore? One answer is that successful thought experiments are grounded. Explaining the nature of this grounding relationship, especially as it applies to ethics, is the main task of this dissertation. A thought experiment is an experiment that occurs in thought. The "thought" label distinguishes it from an ordinary physical experiment, while the "experiment" label distinguishes it from other types of merely analogical, conjectural, or hypothetical reasoning. Many of the components that are necessary for a successful physical experiment are also necessary for a successful thought experiment. A thought experiment, like a physical experiment, must isolate and vary variables in order to answer a question within a given theoretical context. The result of the experiment has repercussions for its theoretical context. The grounding relationship holds between the components of the thought experiment and the theoretical context of the thought experiment. In order for the thought experiment to be successful, both the experimental set-up and our responses to it need to be grounded in the thought experiment's theoretical context. An experimental set-up will be grounded whenever it meets the following conditions. The concepts used must be defined normally, dependent and independent variables must be isolated and relevantly related, and the propositions of the thought experiment (excepting those describing extraneous particulars) must be relevantly related to the given theoretical context and the question under examination. Grounding responses to thought experiments will then be largely a matter of anticipating and disarming distorting influences. Factors influencing responses include the individual's knowledge of the theoretical context, the state of development of that context, the nature of the presentation of the thought experiment, and subjective filters. It is sometimes difficult to ascertain whether a thought experiment in ethics is grounded. This is largely due to the nature of the theoretical context of thought experiments in ethics. In order to assess the relationship of thought experiments in ethics to their theoretical context, I advocate employing a contextualist methodology involving the process of wide reflective equilibrium. While contextualists use this approach to arrive at considered judgements relating to specific ethical problems, I show that wide reflective equilibrium can also be used to examine the grounding of thought experiments. I conclude the dissertation with an examination of the relationship of thought experiments to computer simulations, a study of various common thought experiment distortions, and some tests and methods designed to aid constructing successful thought experiments. / Arts, Faculty of / Philosophy, Department of / Graduate

M.Sc. / An overview of the process of mathematical logic's growth is depicted in this dissertation. Man began at the very beginning, distinguishing only between truth and falsity (a huge leap in those days, and definitely one in the right direction). Like a sound "abc" , ropositional and predicate logic were developed to be the basis for other mathematical logics. One needs to crawl first, before one walks. Given this frame of reference, humans could let their imaginations roam free. The thought of being limited by using only truth and falsity, was not a foreign concept during the beginning of mathematical developments in logic. It did not, therefore, take very long for the first expansions of propositional and predicate logic. As time progressed, so did thoughts, visions and ideas. Soon mathematicians were developing more enhanced logics, such as modal, many-valued and nonmonotonic logics. In fact, modal logic (or the idea behind it) was considered by Aristotle himself. New developments encouraged mathematicians (and people in other fields — for example computer scientists) to broaden their thinking and produce new ideas. Relatively speaking, fuzzy logic is one of the most recent developments. A very powerful logic, given current computer strengths. Fuzzy logic is a system not without drawbacks, even with powerful computers driving fuzzy logic systems. For example, as the number of inputs in a certain system increase, so does the level of complexity, rendering even enormous computers incapable of coping. Currently the success of any fuzzy logic system depends on the model driving it. These models are built by humans, based on a variety of information gathered over time. If, for instance, in medical diagnoses, the reference base says the symptom of a sore throat is associated with an appendix, the diagnoses will certainly be wrong and you might lose your appendix while only suffering a cold. In this day and age we are standing on the verge of a totally computerized environment. The fridge will soon tell you that you are out of milk and that your brand of milk is currently on a special at a specific shop. It will be able to order and pay for new milk. Keeping an open mind, you might be able to envisage a little robot collecting the milk from your front gate, programmed with the ability to judge whether the milk is fresh (by referring to the sellby- date and the smell and colour of the milk). The robot might even be able to tell you to increase your intake of fresh fruit and vegetables as your pale skin color, dark rings under your eyes, your level of fatigue and current intake of these produce indicates a lack thereof. In the case that you did not sleep at all during the night before (dur for instance to a deadline that needed to be met) the robot can decide that this is more than enough reason for your physical appearance and fatigue

About a decade ago, Adam Elga introduced philosophers to an intriguing puzzle. In it, Sleeping Beauty, a perfectly rational agent, undergoes an experiment in which she becomes ignorant of what time it is. This situation is puzzling for two reasons: First, because there are two equally plausible views about how she will change her degree of belief given her situation and, second, because the traditional rules for updating degrees of belief don’t seem to apply to this case. In this dissertation, my goals are to settle the debate concerning this puzzle and to offer a new rule for updating some types of degrees of belief. Regarding the puzzle, I will defend a view called “the Lesser view,” a view largely favorable to the Thirders’ position in the traditional debate on the puzzle. Regarding the general rule for updating, I will present and defend a rule called “Shifted Jeffrey Conditionalization.” My discussions of the above view and rule will complement each other: On the one hand, I defend the Lesser view by making use of Shifted Jeffrey Conditionalization. On the other hand, I test Shifted Jeffrey Conditionalization by applying it to various credal transitions in the Sleeping Beauty problem and revise that rule in accordance with the results of the test application. In the end, I will present and defend an updating rule called “General Shifted Jeffrey Conditionalization,” which I suspect is the general rule for updating one’s degrees of belief in so-called tensed propositions.

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