Contingency and logic

The subject of traditional logic is proposition which takes get "true" or "false" as its truth value. In traditional logic propositions which take "indefinite" truth value, come across, but they are seen as problem and are not used. Propositions with "indef-inite" value sometimes become true and sometimes become false, therefore, they are called "contingent propositions". Contingent propositions are non-necessary proposi-tions. The subject of probability logic is proposition which takes probability values between 0 and 1 instead of their truth values. The subject matter of this thesis is con-tingent propositions and inferences made from these propositions. This thesis has been especially prepared to exhibit that contingent propositions can be used in logic. In this work, we first of all examined dialectical syllogisms. We then investigated the predicates of the propositions with unquantified subjects as to whether they are acci-dental and showed that they can be used in logical inferences. We proved that the propositions beginning with conjunction "but" indicate exception for the propositions about universals. We showed that the truth value of the propositions with "indefi-nite" truth value in the square of opposition can be determined according to the acci-dentality of their predicates. We explained that besides the subject and the predicate, the context should also be expressed, for contingent propositions to get "true" or "false" value.