Logical constant

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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:

Symbol	Corresponding English
	"not"
	"and"
	"or"
	"implies", "if...then"
	"for all"
	"there exists", "for some"
=	"equals"
	"necessary"
	"possible"

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?

[edit] External links

• Stanford Encyclopedia of Philosophy entry on logical constants