The Criterion of Truth and Falsehood of External, Mental, and True Propositions

Proposition, in logics, is a complete declarative compound that is qualified to be true and false. A proposition mainly divides into two types: categorical and conditional. Categorical proposition has its especial divisions, and one of them is dividing it into true, external, and mental propositions. The paper presents the criterion for these three propositions to be true, and discusses that whether that criterion is useful for other propositions or not. Beside main topic, the ideas of some Islamic theologians are considered and analyzed. Then, the topic of "fact-itself" is discussed, and different ideas regarding that issue are presented. The final part explains what Allamah Tabatabaei has stated about "fact-itself".