A unified account of binary and ternary stress, written in the context of metrical theory, aims for a restrictive theory of stress systems in natural languages. In bounded stress systems the distance between stressed syllables is kept to a maximum. Usually, the notion of bounded stress is equated with binary alternation or binarity. In binary stress systems the rhythmic distance between two stressed syllables is at most one stressless syllable, while in ternary systems the maximum distance is at most two stressless syl- lables. Using Optimality Theory Elenbaas aims to contribute to metrical theory by offering a unified account of binary and ternary stress systems. The arguments are based on analyses of the stress systems of Sentani and Finnish. Both languages have a basically binary stress system, in which ternary patterns appear frequently. The analysis of Sentani shows that the anti-lapse constraint, which plays an important role in the analysis of ternary stress systems, and which requires the avoidance of long sequences of unstressed syllables, must be interpreted as a rhythmic constraint, rather than as a parsing constraint. The analysis of Finnish gives independent evidence for this anti-lapse constraint, where it plays a crucial role in creating binary stress patterns.