Market uncertainty and the process of belief formation

Subjective or personal belief formation has been up to now grounded on axioms (e.g., the axioms of Savage) that can be described asintrospection axioms, for they bear only on judgments formed by the individual within himself (e.g., judgments on the ordering of the “acts” in Savage's contribution), excluding every reference to other, possibly external, sources of opinion formation. This current view, linked to the traditional concept ofinstrumental economic rationality, implicitly assumes cognitive capacities that are most of the time out of the reach of any individual. Therefore this view is little or improperly used in the practical world of economics and/or management. An alternative view of belief formation on a market is offered in this article, grounded on a much more modest demand of cognitive capacities from the individual and on a different concept of economic rationality known ascognitive rationality. The model introduces to this end the global concept of market psychology as well as the concept of regular revision of the sets of opinions. Belief formation then appears as a process of deliberation between the individual and the market, rationality emerging within this process as deeply intertwined with the way the individual revises his opinions during the process. The rational treatment of beliefs in view of reaching a decision can consequently be carefully distinguished from their rational formation process.