will permit mutual derivability: any one of the set of parallel units provides a basis for reconstructing any of the others, or for constructing new units on topics yet to be selected. This quality is obviously of great economic importance in training international Volunteers, or commercial, industrial and diplomatic personnel, where each trainee has some clearly defined technical specialty that he must be able to discuss in his new language. Possibly of equal interest, however, are the applications of mutual derivability in enhancing the strength, or socio-topical relevance of teaching in schools and colleges.
The question remains, however, whether this set of materials is merely a mildly interesting tour de force, with no wider significance. Could the same series of basic questions be applied to Thai cooking, or Thai boxing, or malaria control in Lingala, or French cuisine in French? Can the same 'cluster' format that seems to have worked in this program be applied to teaching by Quechua speakers in the Andes? Or to teaching of English by Thais in Thailand?
The answers are not apparent. The general approach of Chapter 4 is only general, and this specific case study describes only one ad hoc solution. Together, however, we hope that they represent a potentially fruitful trend in finding other ad hoc solutions to other problems. Writers of language lessons can do no more than that.
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