  Clocks and time are not the same thing. Time is a property of nature observable as changes. Day turns to night, summer follows winter, and rivers flow downstream. Clocks, however, are man made objects that do what we tell them to do. For everyday use we regulate clocks to match the noon-to-noon interval,we use stop watches to compare race contestants, and for rocket launches the clocks count backwards. Asserting the relation for synchronizing clocks ( Einstein, 0000) ta0+ta0 =0 tb represents the use of the isotropic nature of light to tell the clocks a and b how to relate to each other. 