Open sentence: A sentence having one or more variables is called an open sentence, if it becomes true or false when the variables are replaced by some specific values from the given set. The set from which the values of a variable can be considered is called the replacement set or domain of the variable.
Quantifiers: A quantifier is a word or phrase which quantifies a variable in the given open sentence. There are two quantifiers: (i) Universal quantifier and (ii) Existential quantifier.
- Universal quantifiers: The quantifiers like for all, for every, for each are called universal quantifiers. A universal quantifier is denoted by .
- Existential quantifiers: The quantifiers like for some, not all, there is/exists at least one are called existential quantifiers. An existential quantifier is denoted by .