The authors of model-dependent realism claim that what type of theory may not exist?
Model-dependent realism Model-dependent realism is a view of scientific inquiry that focuses on the role of scientific models of phenomena. It claims reality should be interpreted based upon these models, and where several models overlap in describing a particular subject, multiple, equally valid, realities exist. It claims that it is meaningless to talk about the "true reality" of a model as we can never be "absolutely" certain of anything. The only meaningful thing is the usefulness of the model. The term "model-dependent realism" was coined by Stephen Hawking and Leonard Mlodinow in their 2010 book, "The Grand Design".
Contrastivism Contrastivism, or the contrast theory of meaning is an epistemological theory proposed by Jonathan Schaffer that suggests that knowledge attributions have a ternary structure of the form 'S knows that p rather than q'. This is in contrast to the traditional view whereby knowledge attributions have a binary structure of the form 'S knows that p'. Contrastivism was suggested as an alternative to contextualism. Both are semantic theories that try to explain skepticism using semantic methods.