 Motion is one sort of change, change of spatial position with respect to time. The motion of time, then, must be change of time with respect to … What? If the answer, by analogy with motion, is “time”, one might be rightly puzzled as to how time (or anything else, for that matter) can change with respect to itself. Furthermore, if it is just time again, then the ratio of these two quantities expressing the supposed rate of change is a pure or dimensionless number if the dimensions of the quantities in this ratio cancel. (See Price 1996, p. 13.) A pure number is not a rate of change, although it may represent various rates of change (for instance, 30 meters/second or 30 miles/hour). As Price remarks, “We might just as well say that the ratio of the circumference of a circle to its diameter flows at \(\pi\) seconds per second!”