A Note on Filtration and Granular Reasoning

The filtration method in modal logic is considered to develop a way of formulating an aspect of granular reasoning, which, roughly speaking, means human reasoning based on granularity. The method, however, originates in purely logical problems like decidability. Then, for our purpose, an extended concept of relative filtration is newly introduced using lower and upper approximations in rough set theory. An example of reasoning process using the relative filtration is illustrated.