Brown denies the idea of other authors and historians that the major difference between Einstein and his predecessors is Einstein's rejection of the aether, because it is always possible to add for whatever reason the notion of a privileged frame to special relativity as long as one accepts that it will remain unobservable, and also Poincaré argued that " some day, no doubt, the aether will be thrown aside as useless ". However Brown gave some examples of what in his opinion were the new features in Einstein's work: