We distinguish three qualitatively different types of uncertainty—ethical, option and state space uncertainty—that are distinct from state uncertainty, the empirical uncertainty that is typically measured by a probability function on states of the world. Ethical uncertainty arises if the agent cannot assign precise utilities to consequences. Option uncertainty arises when the agent does not know what precise consequence an act has at every state. Finally, state space uncertainty exists when the agent is unsure how to construct an exhaustive state space. These types of uncertainty are characterised along three dimensions—nature, object and severity—and the relationship between them is examined. We conclude that these different forms of uncertainty cannot be reduced to empirical uncertainty about the state of the world without inducing an increase in its severity.
KeywordsFactual Uncertainty Normative Uncertainty Causal Decision Theorist Evidential Decision Theory Default View
We would like to acknowledge the support of the Arts and Humanities Research Council (Grant Reference: AH/I003118/1), The Netherlands Organisation for Scientific Research (Grant Number 236-20-005), and the Fonds National de la Recherche Luxembourg (Grant Number 09-194). We are grateful to Hykel Hosni and Casey Helgeson for their comments on an earlier draft.
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