Probabilistic Propositional Logic is the Event Semantics for Classical Formal System of Propositional Calculus
The well formed formulars(wffs) in classical formal system of propositional calculus(CPC) are only some formal symbols,whose meanings are given by a interpretation.Probabilistic logic,based on a standard probabilistic space,is the event semantics for CPC,in which set operations are the semantic interpretation for connectives,event functions are the semantic interpretation for wffs,the event(set) inclusion  is the semantic interpretation for logical implication,and the event equality = is the semantic interpretation for logical equivalence.We can perform event calculus instead of probability calculus in CPC.CPC is applicable to probabilistic propositional calculus completely.