A discussion of the nature and process of phonological changes taking places in languages looks specifically at the merging of allophones and the reorganization of phonemes in response to pressures within the phonological system. The hypotheses of economy and reorganization are used to analyze the process of change within a phonological system. Two languages are examined: Uzbek, a Turkic language with a vocalic system derived from classical Chagatay, and a variety of English spoken in Rhode Island. The analysis is illustrated with a three-dimensional model. Both the hypotheses and the space theoretical model are seen as useful in tracing the courses of already-established sound changes. (MSE)