text: **Logical truth**
  Some complex propositions are true independently of the substantive meanings of their parts.[53] In 
  classical logic, for example, the complex proposition "either Mars is red or Mars is not red" is true 
  independent of whether its parts, like the simple proposition "Mars is red", are true or false. In such cases, 
  the truth is called a logical truth: a proposition is logically true if its truth depends only on the logical 
  vocabulary used in it.[54] This means that it is true under all interpretations of its non-logical terms. In 
  some modal logics, this means that the proposition is true in all possible worlds.[55] Some theorists define 
  logic as the study of logical truths.[16] 