Abstract : It has oft been noted that, whilst fiction is distinct from reality, there are important similiarities between the two. This double-edged relationship to reality is also present in the case of counterfactuals : although they refer to non actual situations, the pertinent non actual situations are those which are most similar to reality. However, this dominant perspective relies heavily on the notion of similarity, which is not only elusive, but varies according to the circonstance. Is there a more detailed analysis to be had of the relationship between fiction and reality on the one hand, and counterfactuals and reality on the other ? This dissertation proposes a conceptual framework which offers an enhanced understanding of these relationships, notably by way of an understanding of their dynamics. The development, firstly in the case of the psychology of fiction, and then in the case of counterfactuals, of a careful representation of the state of the relationship at a particular instant, and of a theory of its dynamics, will furnish the tools required not only for a detailed analysis of the relationship between fiction (respectively counterfactuals) and reality at a particular moment, but furthermore for an account of the progression by which this particular relationship, with these particular properties, came into effect.