The Rotuman language has proved a puzzle for linguists since it has some distinctive characteristics that make it difficult to assign to a subgroup within Oceania. There are several reasons for this according to Andrew Pawley, a linguist at Australian National University. In part it is because Rotuman is an isolate, having no very close relatives that can shed light on its development. Complicating the issue is evidence of at least two layers of Polynesian loanwords, mainly from Samoan and Tongan, accounting for some 40 percent of the total vocabulary. In recent years Rotuman has also borrowed heavily from Fijian and English, especially in areas associated with modern culture. Another source of confusion is the fact that the language uses metathesis (the inversion of word-final vowels with immediately preceding consonants) which produces a vowel system that includes umlauting, vowel shortening, and dipthongisation. The result is that an original system of five vowels has increased to ten. Metathesis has increased the rate of change in Rotuman, adding to the problem of its classification. Nevertheless, when Polynesian loan words are stripped away, Pawley finds convincing evidence linking Rotuman to western Fijian (Pawley, 1979).
As a result of metathesis, most Rotuman words have two forms. For example, the word hosa 'flower' becomes hoas in some contexts, the word pija 'rat' sometimes appears as piaj. According to Niko Besnier, the incomplete forms of Rotuman words are derivable from the complete forms through the following processes: (a) a rule of metathesis inverting the order of the last vowel of the word and of the immediately preceding consonant, if there is one; (b) a rule of vocalic assimilation that reduces certain vocalic pairs obtained through metathesis to a single vowel whose phonological characterization is a combination of the distinctive features of the two vowels in the underlying pair; (c) a rule of reduction that changes the first vowel of the other vocalic pairs into a glide, thus reducing the underlying pair to a dipthong; and (d) a rule of length reduction that shortens clusters of similar vowels obtained from (a) to single vowels (Besnier 1987).
Grammatically, the complete form is used to express definiteness, the incomplete form is used to express indefiniteness. For example, 'epa la hoa' 'the mats will be taken' (where 'epa is the complete form) is used in reference to specific mats (definiteness), while 'eap la hoa' 'some mats will be taken' (where 'eap is the incomplete form) is used in reference to any mats (indefiniteness). All content words have definite and indefinite forms (Churchward 1940).
Rotuman has been written in three different orthographies: one devised by early English Methodist missionaries, one by French Roman Catholics, and one by Churchward. The early Methodist orthography is rarely used nowadays. Most Methodists use the Churchward orthography, which is taught in schools. Catholics still use the French-based orthography primarily, although Churchward's orthography has gained increased acceptance, albeit in a modified form. In addition to umlats over 'a', 'o' and 'u', Churchward uses a single dot under the 'a' to designate a sound between 'a' and 'o', and a single dot over the 'a' to designate a sound between 'a' and 'e'. He also uses macrons (dashes) over vowels to indicate lengthening. Rotumans often omit these diacritics in informal writing.
Churchward, C. Maxwell
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Conclusion (translated from the German) of Hans Schmidt's doctoral thesis on the history of the Rotuman language.