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:

Symbol	Corresponding English
$\lnot$	"not"
$\land$	"and"
$\lor$	"or"
$\rightarrow$	"implies", "if...then"
$\forall$	"for all"
$\exists$	"there exists", "for some"
$=$	"equals"

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?

External links

• Stanford Encyclopedia of Philosophy entry on logical constants