Two ill-defined and controversial sound developments of late Old Spanish, namely the asymmetric diphthongizatioris ié > ì and ué > e, become better understandable if one selects as starting points a set of morphological rather than phonological conditions. Both verbal inflection and suffixal derivation can be invoked, including the rivalry of certain characteristic groups of preterits (-iemos, -ieste(s) beside -imos, -iste(s) etc.) and the competition of pairs or clusters of functionally more or less related suffixes: -ero beside -uero, -eño alongside -ueño—in addition to the pressure exerted, in the ranks of hypocoristics, by the close-knit series -ico, -ito and -in(o) on isolated -iello.