Properties as World-Lines : How Fictional Models Are Related to Target Systems

International audienceThe understanding of scientific models as fictions allows to explain the idealizations or abstractions of some models, like those produced, for example, by the analogy between gas molecules and billiard balls in the dynamical theory of gases, highlighted by Marie Hesse. However, this interpretation struggles to explain the predictive success of scientific models, and more generally, the relation between a model as fiction and its real target system. In- deed, the realist correspondence theory of truth cannot hold, notably when a theoretical object is described with idealized properties according to a scientific model. Roman Frigg proposed a fictionalist approach to scientific models based on the notion of make-believe developed by Kendall Walton. Its principle is to compare properties rather than objects themselves; an idealized object of a model does not belong to the same ontological category as a real object of a target system. We agree with that idea because, as Fred Dretske showed, scientific laws describe relations between properties expressed by predicates, and not be- tween extensions of those predicates. But according to Frigg's approach, the comparison between models and reality is possible because the properties of abstract entities and of real objects are the same. In this paper, we will argue that this idea is a kind of correspondence- truth and we will propose to understand properties as world-lines: the real and the fictional properties are not the same, but they are linked by the same world-line. Originally, in this sense a world-line is a concept developed by Jaakko Hintikka to solve the issue concerning the identity of individuals in modal contexts. Here, we will generalize that idea to under- stand the relation between a fictional property of a model entity and a real property of an actual object. Hence, we persist in understanding models as fictions, but propose to explain their success in a new way