| Hi Tom,
I guess that definition of a <Class> (discussed so far) takes into account 4 dimensional world including imaginary worlds (from ISO 15926), rather than 3+1 world. I think that in this case your example is not very clear.
Regards, Alex
David,
I'm ok with <Class> being defined as a set whose set membership criterion does not change -- which is how you have defined it.
But I'm not ok with the membership of a <Class> never changing, and with your claim that apparent change is simply a matter of our discovering a new member that we hadn't recognized as a member before. My reason is that even if set membership criteria do not change, those things which make up the universe of discourse for a <Class>/set do change. For example, if a customer of a tobacco company has to be eighteen years old, then every year there will be a new crop of people (the universe of discourse) who are eligible to become customers; and probably some of them will. This isn't a merely apparent change; it is a change in what you called "true membership".
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