 The second is the problem of contradiction. A naive comprehension principle generates objects that violate the principle of noncontradiction. Consider the condition of being taller than everything. By the naive comprehension principle, this condition determines an object and so there is an object that has exactly the property of being taller than everything. But then it is taller than itself, which is a contradiction given the irreflexivity of the taller than relation. The irreflexivity of the taller than relation is nonlogical. But not so with the identity relation, as = is typically taken to be a logical predicate. It is a logical truth that everything is self-identical; i.e., the sentence ∀x x=x is true under every interpretation. But consider the property of being self-distinct. By the naive comprehension principle this condition determines an object and that object is self-distinct. But then that object does not satisfy the condition x=x. So our logically true sentence has a counterinstance. Contradiction.