近年文獻裡攸關長汀客語聲調衍化的兩大制約，一是一步原則(One Step Principle)－－即衍生調不得再次變調，一是視窗移動制約(Moving Window Constraint)－－即同一個局部視窗至多進行一次二字組變調。在討論範圍擴及東勢客語、天津話、饒平客語、臺灣秘密語、徐州話及北京話的同時，本文提出更具普遍性又可涵蓋視窗移動制約的範疇制約(Domain Constraint)－－即同一個範疇至多進行一次變調，以利逐一檢驗兩大制約的優劣。比較結果呈現拉鋸：兩者皆能解釋東勢客語、天津話和饒平客語。一步原則在長汀客語(Hsu 1994, 1995)及臺灣秘密語勝出；範疇制約取得長汀客語(Chen 2003, Chen et al. 2004)、徐州話快讀與北京話快讀的印證。但是兩者都無法完全掌握天津話快讀。兩大制約的競爭更延燒到藏緬語及虛擬戰場。Hakha Lai的聲調衍化為範疇制約提供了境外奧援，反切語則具現了一步原則在音段衍化的化身。至於兩大制約在非洲聲調語言的表現，且待日後分曉。

This paper aims to further examine two working constraints on tonal derivation proposed in some recent generative studies on Changting, namely One Step Principle (OSP) and Moving Window Constraint (MWC). Our extension of the scope of discussion to other Chinese dialects leads to the necessity of proposing the more general Domain Constraint (DC) which subsumes the MWC. The comparison and contrast between OSP and DC exhibits a see-saw battle at present. Both successfully account for Dongshi Hakka, Tianjin, and Yaoping. OSP wins in Changting (Hsu 1994, 1995) and Taiwanese secret languages, whereas DC wins in Changting (Chen 2003, Chen et al. 2004) and fast speeches in Xuzhou and Standard Mandarin. Different from the above-mentioned cases, Tianjin fast speech demonstrates a dual nature in regard to both constraints. Furthermore, DC receives non-Sinitic support from Hakha Lai; segmental derivation of fanqie languages reveals an OSP counterpart. How these two constraints behave in African tone languages awaits further study.