I've been thinking.. If time is what a clock measures, at what rate does time pass? By definition, the same rate as the clock's hand moves, but that's just circular. Then, there's also "everything is stationary wrt itself", so how does any change occur at all? It just dawned on me that it is related to memory. That is, passage of time or any change can be perceived, because we can compare the current status to the previous one in our memory. If we didn't remember a moment ago, we wouldn't have a concept of time, or life or anything for that matter. So it seems that memory (anything that can store information) must be very important, I didn't realize this before. Does anyone have some thoughts on this, or know of a web site where this line of thought is explored?