7. La décision financière au prisme de la théorie économique, de la finance comportementale et des sciences sociales

Finance is a perfect space from which to observe rationality. Economic theory defines rational financial behavior in a normative way based on the idea of optimal portfolio selection (the CAPM model), and on the stabilizing character of speculation, which leads to an efficient price. Many empirical studies have questioned the relevance of this normative framework. They are at the origin of the field of behavioral finance, which proposes new hypotheses that are more in line with the observations of financial decisions. This field does not question the individualistic approach. In contrast, the social sciences of finance postulate that financiers are social beings like the others, endowed with social capital, belonging to organizations and to social networks, and embedded in political logics. Financial rationality is considered to be socially constructed.