The exact difference between () and ''hua'' is perhaps more uncertain (''fan'' "reaction" and ''huan'' "return" ). In modern Chinese usage, () tends to signify gradual change, transformation or metamorphosis; while ''hua'' tends to mean sudden and profound transmutation or alteration (as in a rapid chemical reaction)—but there is no very strict frontier between the words. () could be used of weather changes, insect metamorphosis, or slow personality transformations; ''hua'' may refer to the transition points in dissolving, liquefying, melting, etc., and to profound decay. () tends to be associated with form (''xing'') and ''hua'' with matter (()). When a snowman melts, the form changes (()) as the snow melts (''hua'') to water. In the Sung dynasty, (Yi ) explained ''bian'' as implying inward change with full or partial conservation of the external Gestalt or form, and ''hua'' as fundamental change in which the outward appearance is also altered. (Needham 1956: 74)

''Hua'' 化 denotes a fundamental and essential change—a transformation. However, sometimes one also encounters the word (), denoting external, momentary, or apparent change. A ''locus classicus'' for this distinction is in the () ...: "The exemplary man (()) changes (()) in accordance with the times without transforming (essence of his being )" ... This in turn permits us to understand the passage in the (neijing suwen'' ) ...: "When the beings take rise (''sheng'' 生 ...), this is called ''hua'' (transformation); when the beings have reached their full development () ... (consequently have taken on a different appearance ), this is called () (change). (Porkert 1978: 44, quoted by Mair 1989: 44)

''Bian'' has the sense of alteration among states of being (for example, from a ''yin'' to a ''yang'' state, or vice versa) or of variation within defined parameters. It differs from ''hua'' 化, "transformation", in implying alternation or variation rather than fundamental and lasting change. The change from a caterpillar to a butterfly, for example, which is both substantive and irreversible, is a frequently cited instance of ''hua'' in the earlier literature. By contrast, a change that involves the realignment of constituent parts in a dynamic system (and that may be or is regularly reversed), such as that from day to night and back again, would be considered an instance of ''bian''. (Major et al. 2010: 871)