Philippe Colo

Can a hearer be rationally justified to have beliefs based on testimony alone when the source of his information is known to have conflicting epistemic goals? When it comes to belief justification, existing theories either recommend avoiding epistemic conflicts of interest or ignoring them. This is an important epistemological limitation. A theory that comes in degrees, capable of explaining what beliefs we are justified to hold and why, despite epistemic conflict of interest, is still lacking. Building on a game-theoretical approach, I suggest such a theory and argue that the hearer can justify some beliefs on testimony alone. This justification relies on an equilibrium concept, which is only reached in the long run. In addition, the hearer’s justified beliefs will always be less accurate than those held by the original source. For instance, assume the speaker is a climate scientist who has good reasons to believe that a 2∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{\circ }$$\end{document}C increase in temperature will lower the current global GDP by 10 percentage points. Under epistemic conflict of interest, a hearer will typically be justified to a belief close to that value, but not equal to it. The smaller the epistemic conflict of interest, the closer, on average, the hearer’s and speaker’s belief. These results highlight the importance of scientific norms which, in practice, are the embodiment of these equilibrium mechanisms and thus of scientific credibility.