Logical constant

In symbolic logic, a logical constant is a symbol that has the same semantic value in all models. Two important types of logical constants are logical connectives and quantifiers. The equality predicate (usually written '=') is also treated as a logical constant in many systems of logic.

Some symbols that are commonly treated as logical constants are:

One of the fundamental questions in the philosophy of logic is "What is a logical constant?"; that is, what special feature of certain constants that makes them logical in nature?