Relativity   Hi ED  Thanks for providing those references  Im sorry these conversations have gotten so combativeprobably both sides could be more cooperative  You clearly know a lot about physics and theres no reason to doubt youre an experienced researcher so I think these disagreements must be somehow based on misunderstandings  Since there are some subtle issues being discussed maybe everyones just butting heads because of miscommunications  Thanks again for the referencesthey help immensely  I dont have any of those texts on hand but I can look them up tomorrow and I do have a few others  After reviewing ResnickHallidayKrane French Goldstein and Marion Thornton one in particular MarionThornton seems to describe the relevant issues clearly  First of all in the section on Newtonian mechanics it mentions Galilean invariance and the principle of Newtonian relativity  Then in the chapter on special relativity we find  The basis of relativity theory is contained in two postulates  but shortly thereafter  Postulate I which Einstein called the principle of relativity is the fundamental basis for the theory of relativity  Postulate II the law of propagation of light follows from Postulate I if we accept as Einstein did that Maxwells equations are fundamental laws of physics  So I think these disagreements have been based on an issue of perspective  If one knows nothing except the principle of relativity then the second postulate is necessaryindeed since Newtonian mechanics satisfies the principle of relativity that principle alone cant lead to SR  Thats why Einstein included the nd postulate  However if we accept EM or the fact that massive particles dont accelarate linearly forever with a constant force mentioned by French or indeed any of the abounding evidence that theres a speed limit in the universe then the full structure of SR can be derived from only the principle of relativity  Do you think thats a reasonable understanding of things  If so maybe we can all work together to find a way to explain things in the article  Id be happy to discuss things further  Regards