Descartes was certain that he was thinking and he was accordingly certain that he existed. Like Descartes, we seem to be more certain of our thoughts and our existence than of anything else. What is less clear is the reason why we are thus certain. Philosophers throughout history have provided different interpretations of the cogito, disagreeing both on the kind of thoughts it characterizes and on the reasons for its cogency. According to what we may call the empiricist interpretation of (...) the cogito, I can only claim to be certain of having experiences, and this certainty, as well as that of my own existence, stems from their phenomenal and subjective character. According to rationalist interpretations, on the other hand, I am certain of having some self-reflexive propositional attitudes, and this certainty derives from their rational features. Psychiatric patients suffering from acute forms of depersonalization or of the Cotard syndrome often doubt that they think and exist, and might even believe that they don't. I argue that their study allows us to favor the empiricist interpretation of the cogito. (shrink)

This thesis develops a novel framework for explaining delusions. In Chapter 1, I introduce the two fundamental challenges posed by delusions: the evidence challenge lies in explaining the flagrant ways delusions flout evidence; and the specificity challenge lies in explaining the fact that patients’ delusions are often about a few specific themes, and patients rarely have a wide range of delusional or odd beliefs. In Chapter 2, I discuss the strengths and weaknesses of current theories of delusions, which typically appeal (...) to one or both of two factors: anomalous experience and reasoning abnormality. I argue that anomalous experience can help explain the specificity of delusions, but has difficulties in addressing the evidence challenge; reasoning abnormality can help address the evidence challenge, but has difficulties in explaining the specificity of delusions. This suggests that there may be an important factor that has not been captured by current theories of delusions. To search for this missing factor, in Chapter 3, I turn to normal believing. Inspired by the literature on Cartesian clarity and phenomenal dogmatism, I develop a dual-force framework of believing, according to which beliefs can be understood as the results of the interaction between the justificatory force and causal force of evidence and the justificatory force and causal force of clear experience, in which something clearly seems to be so to the subject. This framework suggests that the missing factor may be the clear experience with its distinctive phenomenal clarity that compels assent. In Chapter 4, I return to delusions, and argue that the dualforce framework can help us to get a better grip on some personal descriptions of delusions; make progress in addressing the evidence and specificity challenges of delusions; and shed new light on the underpinnings of delusions. In the end, I conclude with some remaining questions for future study. (shrink)