The present project studies the notion of ‘reasonable doubt’, both in its legal sense and as a central issue for reasoning and decision-making in general. The research is interdisciplinary, as it develops at the crossroads of epistemology and the psychology of reasoning, and involves both conceptual analysis and experimental testing.
In everyday life, as well as in the scientific, legal, medical, or policy-making contexts, agents face important decisions, which have to be made based on complex, incomplete, heterogeneous, and sometimes partially contradictory information, coming from different sources with divergent levels of reliability. Despite pervasive uncertainty and conflicting information about climate change, healthy eating, medical or financial risks, for example, practical necessity most often compels us to stop doubting and take action before it is too late.
If my doctor urges me to take a medication with no major recorded side effects, I should probably trust his diagnostic (and follow his advice): doubt would be unreasonable. But what if the side effects of the medication are potentially severe? Shall I rather wait and search for further medical advice? Shall I conduct my own inquiry on the web? Now imagine the doctor herself knows little about a very rare disease which she suspects her patient is suffering from: How is she supposed to negotiate between her own partial ignorance, and her obligation to give clear and intelligible advice to her patient? Everyone is confronted to such questions. Some decisions are life-changing, other are less consequential. However, most situations share the following features: a certain degree of uncertainty, unbounded ignorance and a decision to make.
When is it reasonable to stop doubting and take action based upon a given hypothesis? Is there some threshold, beyond which it would be unreasonable to keep one's mind open to possible alternatives? And how could such threshold be set? How do people, in practice, assess the reasonableness of doubt in different situations, from the most practically consequential to the most theoretical? More fundamentally, what kind of psychological states do 'doubt' and 'belief' refer to in different decisional contexts?
This project tackles such issues from an interdisciplinary perspective, as it develops at the crossroads of epistemology and the psychology of reasoning. As such, it questions both what we should do, if we want to hold rational beliefs, and act rationally, and what people, as agents with limited cognitive abilities, actually do. Moreover, because science and the law are arguably two of the most well-known examples — prima facie thoroughly different from each other — of humans' efforts to design rules of rational method, the project takes as its central domain of study judicial fact-finding and decision-making, and compares the model of judicial reasoning with the much more widely studied model of scientific reasoning, questioning their prima facie obvious differences.
This research hinges upon important societal issues. First, the question of reasonable doubt is of direct relevance for any domain in which agents face complex decision-making situations, involving conflicting information and uncertainties, such as medicine, science, or law. Faced with huge amounts of information from different sources, whose circulation is facilitated by the Internet, citizens must somehow negotiate this tangled web of uncertainty and draw reasonable conclusions. Moreover, ‘open-mindedness’, ‘critical thinking’, and ‘doubt’ are often misused as slogans to question the authority of institutional science in bad faith, as well as by the advocates of those highly unreasonable conjectures that fall under the fuzzy category of “conspiracy theories”. Where does the boundary lie, between epistemic over-cautiousness verging on social paranoia, and the fair stubbornness of the juror embodied by Henry Fonda in Sidney Lumet’s movie Twelve Angry Men, who refuses to convict the defendant without considering any conceivable, even though prima facie implausible, scenario? How are we to account for the ‘common-sense’ intuition, according to which what seems delusional in one case is reasonable in the other?
Prima facie, the notion of ‘reasonable doubt’ seems to be definable in terms of a threshold: depending on what is at stake, one must wait until the hypothesis is confirmed to a certain level before taking action based thereupon. This confirmation threshold, which can be represented probabilistically, seems to depend on the decisional context (particularly the cost of a possible error): jurors in criminal trials should thoroughly consider alternative scenarios before convicting a defendant; doctors or policy-makers, however, may have to take action upon less strongly confirmed hypotheses, depending on the relative costs and benefits of action/inaction.
The overall objective of this project is to explore the limits of such a decision-theoretic view, and to work towards proposing a refined notion of ‘reasonable doubt’. Achieving this objective requires both theoretical analyses, and the development of an experimental programme.
