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Re: [ontolog-forum] The concepts can change?

To: ontolog-forum@xxxxxxxxxxxxxxxx
From: John F Sowa <sowa@xxxxxxxxxxx>
Date: Tue, 17 Jul 2012 16:59:50 -0400
Message-id: <5005D246.8030703@xxxxxxxxxxx>
On 7/17/2012 3:35 PM, Chris Partridge wrote:
> It looks to me as if one can distinguish between (a) terms/classes whose
> definitions (membership conditions) change over time but whose extension
> remains the same across time and (b) terms whose extensions change over
> time, so are probably not classes in any set-theoretic sense.    (01)

For each class, the defining relation is fundamental.  The set
of instances can change at different times, places, and possible
(or actual) worlds.    (02)

> for a standards body at any particular time there is an official definition
> of a metre and so the extension of the class metre at any particular time
> is fixed by the official definition at that time.    (03)

The old standard was the distance between two marks on a bar made
of a platinum-iridium alloy when measured at the melting point of ice.    (04)

The current standard is equal to 1,650,763.73 wavelengths of the
orange-red emission line in the spectrum of a krypton-86 atom
in a vacuum.    (05)

In either case, there is no "instance" of a meter.  The length
of something is always determined by a relation (some procedure
that carries out some kind of comparison).    (06)

Basic principle:  the *relation* is fundamental.    (07)

John    (08)

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