Is not all material theory an otherwise arbitrary symbolic representation of reality in the most convenient/useful manner available?
No. Our representations of the world are
not arbitary.
Let's take a simple example: I have two small marble balls on my desk. Why is that designation not arbitary? Because they behave as a whole - I can pick them up, if they are struck by another ball they will move off as a whole. If I drop they fall as a whole, and bounce as a whole.
I expect you will already have spotted a problem. Namely that some particles from the marble balls will be left behind or chipped off, and other particles from my hands, or from the table, will have merged with the balls. Does this make the designation of the balls arbitary? No. It makes them
fuzzy.
Taking it further: why do we consider the Sun as a whole when it is constantly flining energy and particles into space? Because to understand it's properties and influences we have to. If you didn't consider the sun as a whole you could never understand the effects it had, or the reasons behind the conditions at its surface and centre. Sure you can note that at X degree and Y pressure the hydrogen was fusing - but you could never explain the tempreture or the pressure without the holistic approach.
This is even more true when you start looking at organisms.
In summary, then, our categories are fuzzy, but not arbitary.
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