 It is a plausible requirement on any answer to these questions that two criteria be  respected.[4]  First, a stipulative definition should not enable us to establish essentially new claims—call this the Conservativeness criterion. We should not be able to establish, by means of a mere stipulation, new things about, for example, the moon. It is true that unless this criterion is made precise, it is subject to trivial counterexamples, for the introduction of a definition materially affects some facts. Nonetheless, the criterion can be made precise and defensible, and we shall soon see some ways of doing this.