ABSTRACT
Individual-variables are used in Lower Predicate Calculus formulae in two importantly different ways. As reader used them in Lower Predicate Calculus-2, for example, they are straightforward variables which take names of individuals as values, in just the same way as propositional variables and predicate variables take propositions and predicates respectively as values. When variables are used in the first of these ways, they are said to be free variables. When they are used in the second way, they are said to be bound variables; and a quantifier which contains a certain variable is said to bind all the occurrences of that variable which lie within its scope.
