As you point out, the difference between money and the tooth fairy is between their characteristics and rules. Economic theory then focuses on money, the economy, and their characteristics and rules to develop insights into patterns, behavior, and previously unseen characteristics inherent to economic theory.
Anyone is free to create a theory of tooth fairies and attempt to find similar relevance.
> for the simple reason that money is a human construct
By that reasoning, there's no such thing as "chess theory" either.
> with the end of scarcity
Scarcity ended? Nobody told me!
As you point out, the difference between money and the tooth fairy is between their characteristics and rules. Economic theory then focuses on money, the economy, and their characteristics and rules to develop insights into patterns, behavior, and previously unseen characteristics inherent to economic theory. Anyone is free to create a theory of tooth fairies and attempt to find similar relevance.
Music is a human construct as well and yet: https://en.wikipedia.org/wiki/Music_theory
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