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27. Natural Reality / D. Time / 3. Parts of Time / d. Measuring time

[how we measure intervals and transits of time]

5 ideas
We measure change by time, and time by change, as they are interdefined [Aristotle]
     Full Idea: Not only do we measure change by time, but time by change also, because they are defined by one another.
     From: Aristotle (Physics [c.337 BCE], 220b14)
     A reaction: He defends the idea that time is the 'number' of change, but this idea should sound a warning bell. He rejects the idea that time IS change. It is seems instrumentalist to make the existence of time depend on its measurement.
Circular motion is the most obvious measure of time, and especially the celestial sphere [Aristotle]
     Full Idea: Uniform circular motion is most of all a measure, because the number of this is most easily known. …This is why time is thought to be the motion of the [celestial] sphere, because the other changes are measured by this one.
     From: Aristotle (Physics [c.337 BCE], 223b14)
     A reaction: This makes the year the basic unit of time for the human race. Apparently minutes only became of interest when railway timetables appeared in the 1850s.
If there is no uniform motion, we cannot exactly measure time [Newton]
     Full Idea: It is possible that there is no uniform motion by which time may have an exact measure. All motions can be accelerated and retarded, but the flow of absolute time cannot be changed.
     From: Isaac Newton (Principia Mathematica [1687], Def 8 Schol)
We can never show that two successive periods of time were equal [Locke]
     Full Idea: Two successive lengths of duration, however measured, can never be demonstrated to be equal.
     From: John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 2.14.21)
     A reaction: Nice thought. You can't lay the durations next to one another, the way you can lengths. You can only count the clock ticks, but not be sure whether their speed remained constant.
We use calendars for the order of events, and clocks for their passing [Bardon]
     Full Idea: Roughly speaking, we use calendars to track the order of events in time, and clocks to track changes and the passing of events.
     From: Adrian Bardon (Brief History of the Philosophy of Time [2013], Intro)
     A reaction: So calendars cover the B-Series and clocks the A-Series, showing that this distinction is deeply embedded, and wasn't invented by McTaggart.