模态逻辑命题的限制条件，建立在其内容的肯定或否定其可能性，不可能性，偶然性或必然性基础之上 The classification of propositions on the basis of whether they assert or deny the possibility, impossibility, contingency, or necessity of their content.
换质法推导一个命题的方法 Inference of the obverse of a proposition.
逆命题通过换位得到的命题 A proposition obtained by conversion.
反对命题一种与另一命题相互联系的命题，若后者为正确则前者一定是错误的，但若后者为错误的则前者不一定是正确的 A proposition related to another in such a way that if the latter is true, the former must be false, but if the latter is false, the former is not necessarily true.
