[en] This commentary reflects on the second postulate of special theory of relativity on advent of Michelson-Morley experiment. Of course the experiment could not complete the task doesn’t mean that the velocity of light is not relative though it is finite. The property of the aether or even of vacuum which permits body to have uniform motion without any resistance may play significant role in maintaining the speed of light constant with respect to which is a subject of our investigation and could produce null results in Michelson-Morley experiment. Our attempt is to discover the influence of motion of source on the velocity of light first when both velocities are perpendicular to each other and second when both are parallel. The investigation shows that the light velocity is constant with respect to its source, however, when the source comes in motion; its velocity gets vectorially added to the velocity of light as it happens for all bodies. Moreover the starlight aberration surprisingly supports to the first case which is circumvented yet. In Michelson-Morley experiment, the light source was always rest with respect to the apparatus consequently the speed of light was constant with respect to the apparatus giving no shift in the fringes. (author)