The purpose of this thesis is to establish the part played by tone in the facts and operations of the language. This is achieved by analysing the observed speech-tones. In connected speech several tone-levels are used, but frequently the difference between two of these proves not to be significant. An initial investigation leads to a hypothesis of two essential tones. Prom the behaviour of certain tone-pat terns two distinct kinds of high-tones have to be recognized. The essential tones of basic nominals are discovered by observing their tone-patterns in given contexts. In this way there is established the existence of a single alternance of tone on each lexical syllable, and the absence of any tonal alternance on prefix syllables. Variations occur in the tones of some nominals according to their context, but frequently the tone-patterns are invariable. The tonal behaviour of compound nominals is related to the form as well as to the tones of their components. Where one nominal is based on another there is a close relationship between their tone-patterns. Verbals and nomino-verbals have a tonal behaviour different from that of nominals, but their syllables also display either a single tonal alternance or none at all. Several cases occur where the meaning of a verbal can be determined only when its tones are known. Although tone is not an important factor in indicating syntactical junctions, it often characterizes such Junctions. Interrogative speech is indicated by the use of different intervals between the tone-levels rather than by the use of special tone-patterns. Whether considered lexically, morphologically or syntactically the tones are an integral part of the language which can neither be adequatly analysed her accurately used unless they are taken into account.