 This solution to Russell’s paradox is motivated in large part by adoption of the so-called vicious circle principle. The principle in effect states that no propositional function can be defined prior to specifying the function’s scope of application. In other words, before a function can be defined, one must first specify exactly those objects to which the function will apply (the function’s domain). For example, before defining the predicate “is a prime number,” one first needs to define the collection of objects that might possibly satisfy this predicate, namely the set, \(N\), of natural numbers.