[from the Foreword] The present work describes the results of a research over the semantic value and the functions of the Syriac verbal prefix et- and of the et- conjugations. Also the so-called internal passives will be taken into account, to the extent to which they complete and determine the role of the et- conjugations. The aim of the research was to verify whether, in order to give an exhaustive and coherent picture of the different meanings of the verbal et-stems, it can be useful to introduce into the Syriac verbal system the notion of middle voice.