A Fuzzy Modal Logic for Similarity Reasoning

In this paper we are concerned with the formalization of a similarity-based type of reasoning dealing with expressions of the form approximately ϕ, where ϕis a fuzzy proposition. From a technical point of view we need a fuzzy logic as base logic to deal with the fuzziness of propositions and also we need a modality to account for the notion of approximation or closeness. Therefore we propose a modal fuzzy logic with semantics based on Kripke structures where the accessibility relations are fuzzy similarity relations measuring how similar are the possible worlds.