 More precisely, naïve set theory assumes the so-called naïve or unrestricted Comprehension Axiom, the axiom that for any formula \(\phi(x)\) containing \(x\) as a free variable, there will exist the set \(\{x: \phi(x)\}\) whose members are exactly those objects that satisfy \(\phi(x)\). Thus, if the formula \(\phi(x)\) stands for “\(x\) is prime”, then \(\{x: \phi(x)\}\) will be the set of prime numbers. If \(\phi(x)\) stands for “\({\sim}(x = x)\)”, then \(\{x: \phi(x)\}\) will be the empty set. 