65 A reference grammar for native speakers of Aymara is Ross's Manual aymara para los aymaristas (n.d. [con- siderably after Ross 1953]). Its purpose is to enable Aymara speakers already bilingual and literate in Spanish to learn to read and write Aymara and to become aware of differences between Aymara and Spanish structure which create difficulties for Aymara monolinguals wishing to learn Spanish. As indicated earlier, the CALA writing system used by Ross is designed to familiarize Aymara speakers with Spanish spelling with a view to facilitating their learning to read and write in that language. Accordingly, Spanish loans, even those which entered Aymara hundreds of years ago and are completely adapted to Aymara phonology, are spelled as Spanish and the five vowels of Spanish are used even though Ross recognized that Aymara has a three-vowel system. Evidence that the CALA alphabet does in fact accomplish the objective of making it easier for Aymara monolinguals to learn Spanish is lacking. The Ross Manual is in effect a contrastive study of Spanish and (Missionary) Aymara, often describing Aymara in terms of Spanish, although this is warned against (n.d.:65). The manual is also prescriptive, for example in Lesson IX on punctuation. The grammatical analysis is lacking in some important respects; for instance, the four-person system is not completely