We describe our effort in defining change-of-state words from Core WordNet by constructing axioms anchored in core theories that are crucial in characterizing event words, including change of state, composite entity, scales and event structure. Our methodology consists of three steps: Analyzing the structure of a word's WordNet senses, writing axioms for the most general senses, and testing the axioms on textual entailment pairs. We also describe some common issues we faced and decisions we had to make during axiomatization. We look at two specific textual entailment examples in detail to illustrate the power of this method.