However, Einstein also tried to extend and generalize the special theory of relativity by incorporating version (2) of Mach’s Principle into the general theory of relativity. Einstein was deeply influenced by Mach’s empiricist programme and accepted Mach’s insistence on the primacy of observable facts of experience: only observable facts of experience may be invoked to account for the phenomena of motion. As a consequence, Einstein restricted the concept of relative motions to relative motions b