The evolution of the Middle Chinese checked rù 入-tone (“entering tone” or “rùshēng 入聲”) syllables into the unchecked syllables of present-day Běijīng Mandarin—whose pronunciation is the basis for that of Modern Standard Chinese—has been of particular interest to linguists over the past century for the reason that a clear pattern of development has been hard to discern. Unlike the systematic development of the rù-tone in other Mandarin dialects (Rù-tone Development in Mandarin Dialects), the rù-tone syllables in Běijīng Mandarin until very recently appeared on the surf…