Abstract
I argue that the key to understand many fundamental issues in philosophy of science lies in understanding the subtle relation between the non-empirical cognitive values used in science and the constraints imposed by measurability. In fact, although we are not able to fix the interpretation of a scientific theory through its formulation, I show that measurability puts constraints that can at least exclude some implausible interpretations. This turns out to be enough to define at least one cognitive value that is able to penalize, without damages, precisely those bad features that deceive purely empirical assessments. This leads to the formulation of a simple model of scientific progress, that is based only on empirical accuracy and conciseness. The model is confronted here with many possible objections and with challenging cases of real progress. Although I cannot exclude that the model might be incomplete, it includes all the cases of genuine progress examined here, and no spurious one. In this model, I stress the role of the state of the art, which is the collection of all the theories that are the only legitimate source of scientific predictions. Progress is a global upgrade of the state of the art.