This study is an historical and philosophical analysis of eight major theories that concern music perception, cognition, and meaning. These theories, developed in the 20th century, are among those most often cited by the music psychology and philosophy research literature. Included are Carl Seashore's theory of musical inheritance, Information theory, Mary Louise Serafine's theory of music as thought, music cognition versus speech cognition, neural network and Connectionist theory, and the musical meaning and communication theories of Susanne Langer, Leonard Meyer, and Peter Kivy. The links between these theories and other experimental and philosophical research are considered as well. The final chapter offers a list of 21 principles of music cognition and aesthetic communication derived from the analysis of each theory. The analyses reflect the recent historical development of music psychology and philosophy research, and serve as a useful guide for future investigations.