Predicate Glossary


An n-adic predicate is an expression which yields a sentence when applied to n names or more generally to n referring expressions.


In natural language, a predicate can be seen as the result of removing n names from a sentence, leaving gaps which can be filled by other names to make other sentences.

In the formal language of first order logic, a predicate symbol is an upper case letter representing an arbitrary predicate.

In Logic for Fun, a predicate is a vocabulary item standing for a function mapping the objects in the specified domains (sorts) to truth values (in the domain bool).


  1. In English, 'is a goat' is a monadic (unary) predicate. Applying it to the name 'Billy' yields the sentence 'Billy is a goat.'
  2. Similarly, 'kicks' is a dyadic (binary) predicate. Applying it to the names 'Aristotle' and 'Billy' yields the sentence 'Aristotle kicks Billy.'
  3. In the formula Fa AND NOTRba the letter F is a monadic predicate symbol and R is a dyadic one.