Dynamics of Galois Lattices: The case of epistemic communities Sunbelt, 16-20 février 2005, Redondo Beach, CA. Camille G. Roth, Paul Bourgine Understanding the structure of knowledge communities and particularly the organization of « epistemic communities » (ECs), or groups of agents sharing common knowledge concerns, is usually based on either social relationships of semantic similarity. To link social and semantic aspects, we introduce a formal framework based on Galois lattices that categorizes ECs in an automated and hierarchically structured way, allowing us to rebuild a whole community structure and taxonomy. As the resulting lattice includes all possible ECs it is often voluminous and quite clumsy, we accordingly propose criteria for selecting the most relevant epistemic communities with respect to our rebuilding task – for instance, ECs gathering a certain proportion of agents and thus prototypical of major fields. This process produces a partial lattice yet a yielding and manageable representation of the community structure. From there, the dynamic study of these static partial lattices enables us to describe community taxonomy not only statically but historically. In particular, we rebuild important stylized facts such as field progress or decline, through the variation in the number of agents of the corresponding EC, as well as field generalization or specialization, through the variation in the number of concerns ; and ultimately emergence of new fields – either entirely new fields, or fields made of several subfields (multidisciplinary or interdisciplinary). Our method has eventually been applied to empirical data and has been successfully compared with categories given by domain experts.