 Here we start with our ordinary temporal dimension—what we may have supposed to be the only temporal dimension—the one philosophers have in mind when they say that time passes. Smart supposes that if this dimension of time indeed passes then there must be a rate at which it  passes.[14]  Whether that rate can slow down or speed up or if time always flows at the same rate is not important, but there must be some rate at which it passes, thinks Smart. Now, just as we would measure the speed of a car, say, by measuring how much distance it covers in a given amount of time, so, thinks Smart, we would have to measure the speed at which time itself passes by measuring how much time passes in a given amount of time of some second temporal dimension. While the car covers forty miles of road in the space of an hour, an hour of time passes in the space of, say, two hours of this second temporal dimension. But then, how fast does this second dimension of time pass? We need a third temporal dimension to measure how long it takes for an hour of the second temporal dimension to pass. But how fast does the third temporal dimension pass? And so on, ad infinitum. Smart concludes that time does not pass.