In the Daoist version illustrating the value of emptiness (e.g., "Huainanzi"), the vessel is upright when empty and overturns when full. By contrast, in the Confucian version illustrating the value of the mean (e.g., "Xunzi"), the vessel tilts to one side when empty, remains upright when filled to the middle, and overturns when filled to the brim (1966: 25-26). John Allen Tucker, professor of East Asian history at East Carolina University, says the "zhi" goblet, which repeatedly fills and empties itself, does not remain in any particular condition, its equilibrium exists in disequilibrium, and "zhiyan" "goblet words" are a metaphor for the dialectic in the "Zhuangzi" that goes from one possibility to the next, assuming perspectives often in order to ridicule them, but never clinging to any position itself. This particular goblet is also a Zhuangzian metaphor that expresses the semantic relationship between words and their meanings. "The goblet is like a word, the meaning is like the wine. Though the goblet can hold wine, and a word, meaning, this kind of goblet continuously spills its wine, just as words spill their meaning, and then both wait for another use. But like the goblet, there is no particular meaning which is statically filling the word, never being emptied or renewed." (Tucker 1984: 26). The University of Michigan professor of Chinese literature Shuen-fu Lin correlates "zhi", the empty goblet that does not hold onto anything, with "xin" "heart-mind" and explains how "zhiyan" "goblet words" can adapt the meaning of any term: [T]he "zhi"—a wine vessel used as a metaphor for the mind ["xin"]—is originally empty and gets temporarily filled with liquid—a metaphor for words—which comes from a larger wine container only when the occasion requires one to do so... Since the mind is like the "zhi" vessel without any fixed or constant rules or values of its own stored in there, and takes ideas always from outside when the occasion for speech arises, it will never impose artificial distinctions and discriminations upon things. This is what [is meant by] "mindless"—the "mind" to be done away with here is, of course, the "chengxin" or "fully formed heart/mind" ...