 Beginning in Zend-Avesta Fechner set forth a theory of mind-body relations, which he then expounded in greater detail in his Ueber die Seelenfrage and Elemente der Psychophysik. This theory has been explained in great detail by Michael Heidelberger (2004: 73–115), who regards it as Fechner’s most important contribution to philosophy. There is no necessary connection between this theory and Fechner’s panpsychism: the theory could be true even if human minds where the only minds in the universe; panpsychism is more about the extent rather than the nature of mind.