Synthese DOI 10.1007/s11229-008-9407-6 Reasoning about data and information Abstraction between states and commodities Patrick Allo Received: 31 January 2008 / Accepted: 11 September 2008 © Springer Science+Business Media B.V. 2008 Abstract Cognitive states as well as cognitive commodities play central though distinct roles in our epistemological theories. By being attentive to how a difference in their roles affects our way of referring to them, we can undoubtedly accrue our understanding of the structure and functioning of our main epistemological theories. In this paper we propose an analysis of the dichotomy between states and commodities in terms of the method of abstraction, and more specifically by means of infomorphisms between different ways to classify states of information, information-bases, and evidential situations. Keywords Data · Information · Information flow · Method of abstraction 1 Introduction When one says of an agent that it is ‘informed that p,’ such an attribution is noto- riously ambiguous between making a claim about a particular cognitively valuable commodity that agent might possess, and making a claim about some abstract state of information we use to characterise that agent’s cognitive position. This particular ambiguity is symptomatic of a more general dichotomy between cognitive commo- dities and cognitive states. Drawing the line between these two is not just a matter of conceptual clarification. Quite to the contrary, its elucidation not only forces us to reflect on what we do when we attribute information to someone, but also invites us P. Allo (B ) Centre for Logic and Philosophy of Science, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium e-mail: patrick.allo@vub.ac.be P. Allo IEG, Oxford University, Oxford, UK 123