Did Einstein Use Only Two Postulates to Derive Special Relativity in 1905

Einstein has been credited with deriving special relativity from two postulates, the principle of relativity and the constancy of the speed of light, in his first paper on special relativity in 1905. However, the existence of the Voigt transformation suggests that more than two postulates are needed for deriving the Lorentz transformation. In this study, Einstein’s derivation of the Lorentz transformation is examined for logical consistency and implicit assumptions. It was found that Einstein’s two postulates are insufficient for deriving the Lorentz transformation and essential additional assumptions were used. Because Einstein did not postulate all the necessary conditions, he arrived at the Lorentz transformation due to several logical mistakes caused by using same symbols for different quantities and variables. Therefore, Einstein did not derive special relativity from only two postulates in 1905. Einstein’s most important real contribution to special relativity in his first relativity paper in 1905 is the expulsion of the medium of light waves from modern physics and the reinterpretation of the Lorentz transformation with relative velocity between reference frames instead of velocity relative to ether.