  If absolute time and space cannot serve to distinguish absolute from relative motions — more precisely, absolute from relative changes of motion — empirically, then what can? Newton answers, “The causes which distinguish true motions from relative motions are the forces impressed upon bodies to generate motion. True motion is neither generated nor changed except by forces impressed upon the moving body itself.” The problem then becomes one of distinguishing the forces impressed on bodies, where forces are quantities; and hence the key issue is whether there are theory-mediated measures of them that yield unequivocal values — in contrast to different measures of the same force that yield different values, the hallmark of relative motion. The famous bucket example that follows is offered as illustrating how forces can be distinguished that will then distinguish between true and apparent motion. The final paragraph of the scholium begins and ends as follows: