On the consistency between the assumption of a special system of reference and special

In a previous work, we have shown that the null result of the Michelson– Morley experiment in vacuum is deeply connected with the notion of time. The same is true for the postulate of constancy of the two-way speed of light in vacuum in all frames independently of the state of motion of the emitting body. The argumentation formerly given is very general and has to be true not only within Special Relativity and its “equivalence ” of all inertial frames, but as well as in Lorentz-Poincare ́ scenario of a preferred reference frame. This paper is the second of a trilogy intending to revisit the foundations of Special Relativ-ity, and addresses the question of the constancy of the one-way speed of light and of the differences and similarities between both scenarios. Although they manifestly differ in philosophy, it is debated why and how the assumption of a “special system of reference experimentally inaccessible ” is indeed compati-ble with Einstein’s Special Relativity, as beautifully outlined and discussed by Bell [Speakable and Unspeakable in Quantum Mechanics (Cambridge Univer-sity Press, Cambridge, 1988)]. This rather trivial statement is still astonishin