Yoruba Vowel Patterns: Deriving Asymmetries by the Tension between Opposing Constraints

It is frequently the case that phonological patterns exhibit asymmetric properties with respect to their featural content. Such asymmetries may involve a variety of properties including stability, level of activity, nature of assimilatory target, nature of assimilatory trigger, and nature of epenthetic segment. Consider examples of these properties briefly. With regard to stability, it may be the case, for example, that high tones are stable under deletion while nonhigh tones are not (e.g. Pulleyblank 1986), or that nasality is stable while orality is not (e.g. Prunet 1986). Some features may play an active role in the phonology, while a second feature may be relatively or completely inert. For example, some tongue root harmony systems exhibit active advancement (ATR) while others exhibit active retraction (RTR) (Archangeli & Pulleyblank 1994). Recurrent patterns where one segment type acts as the target of assimilation and another acts as the trigger are attested. For example, coronals are frequently observed to function as assimilation targets while noncoronals frequently function as assimilation triggers (Paradis & Prunet 1991). As a final example, certain features may more typically characterise epenthetic segments (Archangeli 1988): high vowels may be more frequently epenthesised than mid, front more frequently than back, oral more frequently than nasal, and so on.