Ternary stress presents a unique challenge to constraint-based metrical stress theories. The main question is how to model ternarity without ternary-specific representations, such as ternary feet.1 Along this line of reasoning, Elenbaas and Kager (1999) interpret ternarity as an underparsing effect in which long lapses are avoided while the number of feet is kept to a minimum. The standard constraint that prohibits long lapses is *LAPSE (1). This constraint is also known as *EXTENDEDLAPSE (Gordon 2002) or *LONGLAPSE (Kager 2007).
The constraint *LAPSE is a markedness constraint that disfavors sequences of three adjacent unstressed syllables (or moras). This constraint only triggers ternary rhythm when interacting with PARSE-σ (≡ Syllables must be footed) and the alignment constraints ALLFEET-R/L.
Let us illustrate with Cayuvava, a ternary-stress language (Key 1967)....