Logical Perspectives on Informational Social Influence in Trade and Science

The Ph.D. thesis studies two concrete social phenomena where information and in particular higher-order information play a key role:

1. Scientists who acquire knowledge and belief through observation and interaction
2. Traders who reason about asset values and about other traders. Using the machinery of dynamic epistemic logic (DEL) the thesis formulates and structurally analyses opinion diffusion in scientific communities and so-called greater fools reasoning in trade markets – one important mechanism used in the explanation of financial bubbles.

In particular, the thesis focuses on informational social influence: People are under informational social influence when they accept information obtained from someone else as evidence about reality.
Alongside these applied analyses, the thesis also makes two contributions that are more theoretical:

1. A representation theorem for one particular family of information update models
2. A philosophical reflection on the method of logical modelling used in the rest of the thesis.

I argue that epistemic logic is a natural and expressive framework to study informational social influence, as epistemic logic allows abstracting away from irrelevant details and at the same time focus on informational content of social influence such as higher-order reasoning and information change. The thesis thereby shows that an epistemic logical study provides a novel perspective on well-known problems of informational social influence.