So, what is time? To put it simply, time is duration. Our clocks mark change or, more precisely, our timepieces are benchmarks of change that indicate the passage of time. We could say, then, that time is a necessary precondition for change, and change is a sufficient condition to establish the passage of time. In other words, whenever there’s a change of any kind, we know that time has passed. We see this as we go through life and as we age. And we cannot recover the minutes that have passed by.