Working within a branch of experimental psychology called psychophysics, scholars argue about "just noticeable differences," thresholds of perception, and related postulations. Consider the volume of sound as an issue. It seems intuitively there should be sounds that are different from one another in an objective sense (mechanically measurable) in that one is louder than the other, but that are not perceived as different by human beings. After all, we did not evolve as mechanisms for the precise measurement of sound, We evolved, to be simple about it, to survive and reproduce. That does not require ideally good distinctions in these matters. So there should be some just noticeable difference between sound A and sound B as to volume, such that if I hear any pair closer in volume to each other than those two, I will perceive them as identical. Right? Likewise with weights? Put one object in my left and put another in my right and ask me to tell you which is heavier....