Yet when it comes to more reflective judgments, people go beyond the outcome of a similarity comparison.
In other words, C and D embody differing modes of presentation. A natural suggestion is to regard all of these as being beliefs.
For example, Michael Dummett cautions against trying to explain knowledge of a first language on the model of knowledge of a second language. Feature-based theories of concepts, such as prototype theory, seem to have particular difficulty explaining the phenomenon of coherence, since they are inherently unconstrained and allow any set of properties to be lumped together to form a category, whereas our concepts often appear to represent categories as involving more than merely sets of ad hoc co-instantiated properties.
Of course, this just raises the question of what sort of structure conceptual cores have.
Many advocates of RTM take the mental representations involved in beliefs and other propositional attitudes to have internal structure. If thought is compositional, and concepts are the constituents of thoughts, then whatever concepts are must also be compositional.