The immediate subject of this work is the semantics of a syntactically- defined set of Tamil verbs, all but one of which are used as main verbs as well as auxiliaries. Those which are discussed in most detail are kiTu. viTu. kiTTiru, iru, vai and vecciru. Mentioned in somewhat less detail are kiTTuvaa, kiTTupoo, vaa, poo (in two meanings), aaku and tole. In setting out to investigate these forms, certain limitations of the traditional methods of linguistic investigation became apparent. With the hope of obtaining more reliable information than was available from regular informants, a series of questionnaires was devised and administered to a total of 117 people from 27 villages in the Chidambaram Taluk of Tamilnadu. It is hoped that the account given here of the use of an interrelated series of questionnaires for the detailed investigation of a specified area of a language will contribute to the methodological basis on which linguistic investigation is founded. From the results of this investigation, it was found that a study of Tamil auxiliary verbs is relevant to certain general points of interest within current linguistic theory. Evidence is presented in favour of the separation of syntax and semantics, on the close relationship between auxiliary and main verbs, and on the need within a linguistic theory for devices to handle gradation.