A large-scale study is reported whose purpose was to elucidate the historical development of the European major and minor modes. The study involved 455 musical works by 259 composers sampled across the years 1400 to 1750. Beginning with the period 1700-1750, a series of statistical studies was carried out on the distribution of scale tones, progressively moving backward in time. The method utilized a modified method of key determination – generalized to handle an arbitrary number of modal classifications. The results from cluster analyses on this data are consistent with the view that the modern major and minor modes have changed over time and were preceded by a system in which there were more than just two modes.