 The second requirement underlines a difference between the definiens and the definiendum, expressed in Tibetan in terms of the first being “substantially existent,” the second “nominally existent.” The latter thus depends on the understanding of something else—here the definiens. According to the third requirement, definiens and definiendum must be co-extensive, but only a single definiens provides the specific denotation of the definiendum. For instance, “causally efficient” is not the definiens of “impermanent” even though everything that is causally efficient is impermanent and vice-versa, because it is not held to be directly contradictory to “permanent,” the way “not remaining for a second moment” (the accepted definiens of “impermanent”) is.