Thomas Byrne

Metaphysicians and cosmologists often make bold, surprising claims about the universe. It is bigger, older, full of more things, more intricately interconnected, than most of us ever thought. Supposing they are correct, does that have any bearing on what we ought to believe about everyday matters, and on what we ought to feel, want, and do in everyday contexts? Many philosophers have been explicitly or implicitly committed to answering ‘no’ to this question. This book argues for ‘yes’. If advocates of chaos theory are correct, then we should rethink how we ought to feel about past evil actions. We ought to feel the positive analogue of regret toward almost everything that has ever been done. If advocates of plenitudinous material ontologies are correct, then we should rethink how we ought to feel about our own suffering versus the suffering of others, and what we ought to believe about where we are and who we are. If advocates of spatial and material infinity are correct, then we should rethink how we ought to treat strangers. Whether and how we ought to help them depends in surprising ways on how much we know about them. In sum, bold claims in metaphysics and cosmology matter.

Predictable polarization is everywhere: we can often predict how people’s opinions, including our own, will shift over time. Extant theories either neglect the fact that we can predict our own polarization, or explain it through irrational mechanisms. They needn’t. Empirical studies suggest that polarization is predictable when evidence is ambiguous, that is, when the rational response is not obvious. I show how Bayesians should model such ambiguity and then prove that—assuming rational updates are those which obey the value of evidence—ambiguity is necessary and sufficient for the rationality of predictable polarization. The main theoretical result is that there can be a series of such updates, each of which is individually expected to make you more accurate, but which together will predictably polarize you. Polarization results from asymmetric increases in accuracy. This mechanism is not only theoretically possible, but empirically plausible. I argue that cognitive search—searching a cognitively accessible space for a particular item—often yields asymmetrically ambiguous evidence, I present an experiment supporting its polarizing effects, and I use simulations to show how it can explain two of the core causes of polarization: confirmation bias and the group polarization effect.

Do people tend to be overconfident? Many think so. They’ve run studies on whether people are calibrated: whether their average confidence in their opinions matches the proportion of those opinions that are true. Under certain conditions, people are systematically ‘over-calibrated’—for example, of the opinions they’re 80% confident in, only 60% are true. From this empirical over-calibration, it’s inferred that people are irrationally overconfident. My question: When and why is this inference warranted? Answering it requires articulating a general connection between being rational and being right—something extant studies have not done. I show how to do so using the notion of deference. This provides a theoretical foundation for calibration research, but also reveals a flaw: the connection between being rational and being right is much weaker than is standardly assumed, since rational people can often be expected to be miscalibrated. Thus we can’t test whether people are overconfident by simply testing whether they are over-calibrated; instead, we must try to predict the rational deviations from calibration, and then compare those predictions to people’s performance. I show how this can be done—and that doing so complicates the interpretation of robust empirical effects.