How much do we know about reasoning about subjective concepts? Bayes' law tells you how probable you should consider any given black-and-white no-room-for-interpretation statement, but it doesn't tell you when you should come up with a new subjective concept, nor (I think) what to do once you've got one.
You may be interested in the literature on "concept learning", a topic in computational cognitive science. Researchers in this field have sought to formalize the notion of a concept, and to develop methods for learning these concepts from data. (The concepts learned will depend on which specific data the agent encounters, and so this captures the some of the subjectivity you are looking for.)
In this literature, concepts are usually treated as probability distributions over objects in the world. If you google "concept learning" you should find some stuff.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.