to a constant to be a syntax error, while in other languages they are considered syntactically the same (both simply an identifier), and the difference in treatment is semantic (assignment to an identifier is syntactically valid, but if the identifier is a constant it is semantically invalid).

A constant value is defined once and can be referenced many times throughout a program. Using a constant instead of specifying the same value multiple times can simplify code maintenance (as in don't repeat yourself)