Formalization is a fundamental issue in philosophical logic, and its nature has been examined vastly by logicians. It can be defined, in a sense, as a formal analysis of propositions and arguments, without considering their sense, in order to reveal their logical structure. Concerning the notions of function and variable in mathematics as well as the distinction between concept and object, Frege-the founder of modern logic-analyzed a proposition into two parts: predicative (unsaturated) and non-predicative (saturated); and the very analysis is the base of formalization in modern logic.However, validity of the arguments is the target of formalization, since validity-preserving guarantees the soundness of formalization. Logical constants are fundamental elements in logical structures and have a very important role in formalization. However, logicians proposed different criteria for their determination, each of which results in a change in the method of formalization in logic. In this article we show that different logical systems may have different criteria for their logical constants and whether we are to establish a system or want to extend its logical constant affects our decision concerning those criteria.