The role of the iambic-trochaic law in iambicity and
monosyllabization in Mainland Southeast Asia
Marc Brunelle Pittayawat Pittayaporn
University of Ottawa Chulalongkorn University
It has long been noted that Mainland Southeast Asian languages have a tendency towards
iambicity. Iambs, often realized as sesquisyllables, can be reconstructed for most of the proto-languages
of the area (Tai, Mon-Khmer, Sino-Tibetan). Another common trend in the area is the evolution of
sesquisyllabic systems towards monosyllabicity (Alieva 1994; Ferlus 1996; Ferlus 1997; Thach 1999;
Thurgood 1999; Brunelle 2008; Brunelle 2009). These processes manifest two asymmetries in diachrony
of prosodic shift. First, while some originally trochaic languages have become iambic (Thurgood 1999;
Pittayaporn 2005), the converse change, from iambs to trochees, is much less frequent and only
attested in reconstructions (Donegan 1993; Donegan and Stampe 2002; Donegan and Stampe 2004).
Secondly, while iambic systems often become monosyllabic, there are to our knowledge no clear cases
of trochaic systems following a similar path.
The general path towards iambicity and monosyllabicity has often been attributed to language
contact. Although it is likely that contact strengthens internal change, we propose that general
properties of prosodic systems, combined with phonetic drift, are sufficient to account for the two
asymmetries noted above. Most relevant is a strong universal preference for balanced trochees and
unbalanced iambs. This has been formulated as the iambic-trochaic law (Hayes 1985; Hayes 1995),
which ranks feet according to their relative well-formedness, as schematized in (1), where H=heavy,
L=light, bold=stress and “>” = better than :
(1) Iambs (LH) > (H), (LL) > (L) *HL
Trochees (LL), (H) > (HL) > (L) *LH
Due to the prevalence of disyllabic and monosyllabic prosodic systems in Mainland Southeast
Asia, the area is an ideal test-ground for assessing the effects of the iamb-trochaic law on diachronic
shifts. Irrespective of the motivation for this law (Hayes 1985; Prince 1990; Kager 1993; Hayes 1995;
Revithiadou 2004; Hay and Diehl 2007), the distribution in (1) accounts for the directionality of prosodic
change in Mainland Southeast Asia. First, a trochee, be it (LL) or (H), may undergo a stress-shift and
become a well-formed, though not ideal iamb (H) or (LL). However, an iamb that goes through a similar
stress-shift would become an ill-formed trochee (*LH). Secondly, ideal iambs (LH), i.e. sesquisyllables,
can undergo phonetic erosion and become monosyllables (H) without violating the iambic-trochaic law.
Ideal disyllabic trochees (LL), on the other hand, are unlikely to become monosyllabic because such
erosion would yield a strongly dispreferred foot (L). In contrast, this model claims that
monosyllabization of unbalanced trochees is a likely change. This is because loosing the unstressed light
syllable in an unbalanced trochee yields a better foot according to the trochaic-iambic law (H) > (HL).
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