Group Knowledge in Interrogative Epistemology
Alexandru Baltag, Rachel Boddy, Sonja Smets

Abstract:
In this paper we formalize an approach to knowledge that we call Interrogative Epistemology, in the spirit of Hintikka's "interrogative model" of knowledge. According to our approach, an agent's knowledge is shaped and limited by her interrogative agenda (as defined by her fundamental questions or "epistemic issues"). The dynamic correlate of this postulate is our Selective Learning principle: the agent's agenda limits her potential for knowledge-acquisition. Only meaningful information, that is relevant to one's issues, can really be learnt. We use this approach to propose a new perspective on group knowledge, understood in terms of the epistemic potential of a group of agents: the knowledge that the group may come to possess in common (and thus act upon in a coordinated manner) after all members share their individual information. We argue that the standard notions of group knowledge studied in the literature, ranging from distributed knowledge to common knowledge, do not give us a good measure of a group's epistemic potential. Common knowledge is too weak and too "static", focusing on what the agents can coordinate upon only based on their actual, current knowledge (without any intra-group communication), thus disregarding testimonial knowledge. In contrast, the concept of distributed knowledge is too strong, being based on the assumption that agents can completely internalize all the testimonial evidence received from others, irrespective of the limitations posed by their own interrogative agendas. We show that a group's true epistemic potential typically lies in between common knowledge and distributed knowledge. We propose a logical formalization of these concepts, which comes together with a complete axiomatization, and we use this setting to explain both the triumphs and the failures of collective knowledge, treating examples that range from "collective scientific knowledge" (Wray, 2007; Rolin, 2008; Fagan, 2012) to the so-called "curse of the committee".