The field of study of this paper is the analysis of the exchange between two subjects. Circumscribed to the micro dimension, it is however expanded with respect to standard economic theory by introducing both the dimension of power and the motivation to exchange.<br />The basic reference is made by the reflections of those economists, preeminently John Kenneth Galbraith, who criticize the removal from the neoclassical economy of the &ldquo;power&rdquo; dimension. We have also referred to the criticism that Galbraith, among others, makes to the assumption of neoclassical economists that the &ldquo;motivation&rdquo; in exchanges is solely linked to the reward, to the money obtained in the exchange. In the construction of a mathematical model we paid great attention to its usability in field testing.