We analyse how the concept of the ether, playing the role of absolute space, is still present in physics. When the problem is considered in the context of classical mechanics, we show that vestiges of absolute space can be found in the standard presentation of inertial systems. We offer an alternative -- fully relational -- definition of inertial systems which not only eliminates the problem but it further shows that the equivalence principle is just a particular consequence of the No Arbitrariness Principle. In terms of Special Relativity, the non-existence of relative velocities implies a constructive contradiction (their existence is assumed in the construction). The problem is inherited from Lorentz' use of the ether, developed in his interpretation of Maxwell's electrodynamics. In summary, the velocities in the Lorentz transformations must be considered velocities relative to the ether (absolute space) if the theory is not to fall apart for being inconsistent. We discuss the relevance of the phenomenological map, and how previous works have failed to acknowledge that the consistency problem is not in the exposed part of the theory but in the supporting phenomenological map which, rather than being constructed anew, it transports concepts of classical mechanics by habit, without revising their validity in the context of Special Relativity