Lamba: harmony and palatalization

The following data illustrate the interaction between a rule of vowel harmony and a palatalization rule in the language Lamba (Zambia):

In order to see what these data show, we must first understand the morphological structure of these words, a step which leads us to realize that the pronunciation of certain morphemes changes, depending on their phonetic context. Verbs in Lamba are composed of a root of the form CV(C)C, an optional derivational affix marking passive, neuter, applied or reciprocal, and a word-final suffix -a which marks the form as being a verb. The underlying forms of the passive and reciprocal suffixes are clearly -w- and -an-, since they exhibit no phonetic variations. The neuter and applied suffixes appear phonetically as -ik- and -ek-, -il- and -el-. The choice of vowel in the suffix is determined by the vowel which precedes the suffix: if the verb root contains the vowel i, u, or a the suffix has the vowel i, and if the root contains the vowel e or o the suffix has the vowel e. The group of vowels i, u, a is not a natural phonetic class, so it is implausible that the suffixes are underlyingly -el- and -ek- with -il- and -ik- being derived by a rule. The class of vowels e, o is the phonetic class of mid vowels; it is thus evident that this language has a vowel harmony rule which assimilates underlying high vowels (in the suffixes /il/ and /ik/) to mid vowels when they are preceded by mid vowels.

There is an alternation in the realization of certain root-final consonants. As shown in examples such as kaka ~ kat ʃ ika and lasa ~ laʃika, the velar consonants and the alveolar continuant s become alveopalatals when they are followed by the vowel i, by processes of palatalization. It is difficult to express a change of /k/ and /s/ to alveopalatal by one rule without including /t/ – which does not change, see [patika] – so two separate rules are needed.

The interaction between these processes is seen in words which could in principle undergo both of these processes: roots with the vowel e or o, and the final consonant k or s. The example sekeka ‘laugh at’ from /sek-ik-a/ shows how these processes interact. Suppose, first, that palatalization were to apply before vowel harmony. Since the underlying representation has the sequence /ki/ which is required by palatalization, that rule would apply. Subsequently, vowel harmony would assimilate /i/ to [e] after /e/, giving the wrong surface result. This is illustrated below in a derivation which spells out the results of applying first palatalization, then height harmony.

Thus, applying the rules in this order gives the wrong results: this order cannot be correct.

On the other hand, if we apply the processes in the other order, with height harmony applying before palatalization, then the correct form is generated.