A POSSIBLE WORLD SEMANTICS FOR CONDITIONAL LOGIC BASED ON SIMILARITY RELATIONS

In the paper I present and discuss a development of Lewis comparative similarity semantics for conditional logic based on a material or algorithmic definition of the similarity relation between possible worlds. Four conditionals are defined: conceptual, physical, actual and contingent implication, the first, second and third corresponding to Lewis ’ VW logic, the last one to Lewis ’ VC logic. I. Syntax The conditional statements in natural languages are usually reduced to two general types: subjunctive and indicative1 (and, perhaps, some special subtype as counterlegals, might-conditionals, even-kind conditionals...). An example of a subjunctive statement is “If the windows were open the temperature would be lower”, which Lewis ’ theory claims to model in his counterfactual logic [6]. An example of an indicative statement is “If it rains the streets are wet”, which belongs to the class of sentences Burks tries to model with his system of causal statements [2]. A brief description of the two types can be found in the table: Context- Covering Related to Related to Stability dependent more than the the actual Firmness one physical state of situation structure thing