This is the fourth volume of the second edition of the now classic book The Topos of Music. The author presents appendices with background material on sound and auditory physiology; mathematical basics such as sets, relations, transformations, algebraic geometry, and categories; complements in physics, including a discussion on string theory; and tables with chord classes and modulation steps.

Preface to the Second Edition.- Preface.- Part XX Appendix: Sound.- Part XXI Appendix: Mathematical Basics.- Part XXII Appendix: Complements in Physics.- Part XXIII Appendix: Tables.- Part XXIV References and Index.