One of the logic defined by Richard Epstein in a context of an analysis of subject matter relationship is Symmetric Relatedness Logic S. In the monograph [2] we can find some open problems concerning relatedness logic, a Post-style completeness theorem for logic S is one of them. Our paper introduces a solution of this metalogical issue.
In this paper, we bring up the problem of logical omniscience in epistemic logic. One way of avoiding the problem is through Rantala models, where non-normal worlds are introduced. Such models are vulnerable to criticism, as we show. One of many issues that occur is the Bjerring result, which states that incorporating non-normal worlds makes the agent logically incompetent. For this reason, we propose a different solution based on positional logics.
We define and investigate from a logical point of view a family of consequence relations defined in probabilistic terms. We call them relations of supporting, and write: |≈w where w is a probability function on a Boolean language. A |≈w B iff the fact that A is the case does not decrease a probability of being B the case. Finally, we examine the intersection of |≈w , for all w, and give some formal properties of it.
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