Definition:Variable/Propositional Logic
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Definition
A statement variable is a variable which is used to stand for an arbitrary and unspecified statement.
For a statement variable, a lowercase letter is usually used, for example:
- $p, q, r, \ldots{}$, and so on
or lowercase Greek letters, for example:
- $\phi, \psi, \chi$ and so on.
The citing of a statement variable can be interpreted as an assertion that the statement represented by that symbol is true.
That is:
- $p$
means
- $p \text { is true}$
Also known as
Equivalent terms for statement variable are:
- sentential variable
- propositional variable
- sentence letter
- proposition symbol or propositional symbol.
The latter name is also used for the letters of the language of propositional logic, which are intended to represent statement variables.
Some sources use just variable, and rely upon the context for clarity.
Also see
- Definition:Statement Label: Note the difference between this and a statement variable:
- Definition:Propositional Symbol: when propositional logic is developed as a formal language, a statement variable is specified precisely.
- Results about statement variables can be found here.
Sources
- 1946: Alfred Tarski: Introduction to Logic and to the Methodology of Deductive Sciences (2nd ed.) ... (previous) ... (next): $\S \text{II}.12$: Laws of sentential calculus
- 1959: A.H. Basson and D.J. O'Connor: Introduction to Symbolic Logic (3rd ed.) ... (previous) ... (next): $\S 2.3$: Basic Truth-Tables of the Propositional Calculus
- 1964: Donald Kalish and Richard Montague: Logic: Techniques of Formal Reasoning ... (previous) ... (next): $\text{I}$: 'NOT' and 'IF': $\S 1$
- 1965: E.J. Lemmon: Beginning Logic ... (previous) ... (next): Chapter $1$: The Propositional Calculus $1$: $2$ Conditionals and Negation
- 1973: Irving M. Copi: Symbolic Logic (4th ed.) ... (previous) ... (next): $2$ Arguments Containing Compound Statements: $2.3$: Argument Forms and Truth Tables
- 1980: D.J. O'Connor and Betty Powell: Elementary Logic ... (previous) ... (next): $\S \text{I}: 1$: The Logic of Statements $(1)$
- 1988: Alan G. Hamilton: Logic for Mathematicians (2nd ed.) ... (previous) ... (next): $\S 1$: Informal statement calculus: $\S 1.1$: Statements and connectives
- 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): variable: 2.
- 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): variable: 2.