---
tag: Q8ZEXA1KE6
kind: concept
name: Predicate variable
aliases: [relation-symbol]
sources:
  - wikipedia: en:1011332@r1278688980
    locator: Predicate variable
    note: adopted
    mention: wikipedia://en/1011332
    sections: [Summary]
same_as:
  wikidata: Q10531432
  wikipedia: Predicate variable
inventory: [GZHAV92526]
---

## Summary

In mathematical logic, a **predicate variable** is a predicate letter which functions as a "placeholder" for a relation (between terms), but which has not been specifically assigned any particular relation (or meaning). Common symbols for denoting predicate variables include capital roman letters such as $P$, $Q$ and $R$, or lower case roman letters, e.g., $x$. In [[first-order logic|086QKPF0A6]], they can be more properly called metalinguistic variables. In higher-order logic, predicate variables correspond to propositional variables which can stand for well-formed formulas of the same logic, and such variables can be quantified by means of (at least) second-order [[quantifiers|0FYQMKFE77]].