Topics covered in the work include almost all essential problems of theoretical phonology. The author establishes a set of basic concepts which define almost all other concepts of phonology, and gives an axiomatic characterisation of these concepts. The notion of a unit-length segment is analysed and defined, and a precise formulation of the principles of distribution is given. The author offers a formal analysis of the notion of a phoneme, and finally formulates and discusses fundamental hypotheses of phonology.