Representing reality The ontology of scientific models and their representational function.

Today most philosophers of science believe that models play a central role in science and that one of the main functions of scientific models is to represent systems in the world. Despite much talk of models and representation, however, it is not yet clear what representation in this context amounts to nor what conditions a certain model needs to meet in order to be a representation of a certain system. In this thesis, I address these two questions. First, I will distinguish three senses in which something, a vehicle, can be said to be a representation of something else, a target-which I will call respectively denotation, epistemic representation, and faithful epistemic representation-and I will argue that the last two senses are the most important in this context. I will then outline a general account of what makes a vehicle an epistemic representation of a certain target for a certain user-which, according to the account I defend, is the fact that a user adopts what I call an interpretation of the vehicle in terms of the target-and of what makes an epistemic representation of a certain target a faithful epistemic representation of it-which, according to the account I defend, is a specific sort of structural similarity between the vehicle and the target.