In logic and model theory, a valuation can be:
- In propositional logic, an assignment of truth values to propositional variables, with a corresponding assignment of truth values to all propositional formulas with those variables.
- In first-order logic and higher-order logics, a structure, (the interpretation) and the corresponding assignment of a truth value to each sentence in the language for that structure (the valuation proper). The interpretation must be a homomorphism, while valuation is simply a function.
Mathematical logic
In mathematical logic (especially model theory), a valuation is an assignment of truth values to formal sentences that follows a truth schema. Valuations are also called truth assignments.
In propositional logic, there are no quantifiers, and formulas are built from propositional variables using logical connectives. In this context, a valuation begins with an assignment of a truth value to each propositional variable. This assignment can be uniquely extended to an assignment of truth values to all propositional formulas.
In first-order logic, a language consists of a collection of constant symbols, a collection of function symbols, and a collection of relation symbols. Formulas are built out of atomic formulas using logical connectives and quantifiers. A structure consists of a set (domain of discourse) that determines the range of the quantifiers, along with interpretations of the constant, function, and relation symbols in the language. Corresponding to each structure is a unique truth assignment for all sentences (formulas with no free variables) in the language.
Notation
If v {\displaystyle v} is a valuation, that is, a mapping from the atoms to the set { t , f } {\displaystyle \{t,f\}} , then the double-bracket notation is commonly used to denote a valuation; that is, v ( ϕ ) = [ [ ϕ ] ] v {\displaystyle v(\phi )=[\![\phi ]\!]_{v}} for a proposition ϕ {\displaystyle \phi } .1
See also
- Rasiowa, Helena; Sikorski, Roman (1970), The Mathematics of Metamathematics (3rd ed.), Warsaw: PWN, chapter 6 Algebra of formalized languages.
- J. Michael Dunn; Gary M. Hardegree (2001). Algebraic methods in philosophical logic. Oxford University Press. p. 155. ISBN 978-0-19-853192-0.
References
Dirk van Dalen, (2004) Logic and Structure, Springer Universitext, (see section 1.2) ISBN 978-3-540-20879-2 /wiki/ISBN_(identifier) ↩