Because one is true in all circumstances and the other isn’t? What are you actually objecting to? That physical theories can be more fundamental than each other?
I admit that some definitions can be better than others. A whale lives underwater, but that’s about the only thing it has in common with a fish, and it has everything else in common with a whale. You could still make a word to mean “animal that lives underwater”. There are cases where where it lives is so important that that alone is sufficient to make a word for it. If you met someone who used the word “fish” to mean “animal that lives underwater”, and used it in contexts where it was clear what it meant (like among other people who also used it that way), you might be able to convince them to change their definition, but you’d need a better argument than “my definition is always true, whereas yours is only true in the special case that the fish is not a mammal”.
The distinction here goes deeper than calling a whale a fish (I do agree with the content of the linked essay).
If a layperson asks me what temperature is, I’ll say something like, “It has to do with how energetic something is” or even “something’s tendency to burn you”. But I would never say “It’s the average kinetic energy of the translational degrees of freedom of the system” because they don’t know what most of those words mean. That latter definition is almost always used in the context of, essentially, undergraduate problem sets as a convenient fiction for approximating the real temperature of monatomic ideal gases—which, again, is usually a stepping stone to the thermodynamic definition of temperature as a partial derivative of entropy.
Alternatively, we could just have temperature(lay person) and temperature(precise). I will always insist on temperature(precise) being the entropic definition. And I have no problem with people choosing whatever definition they want for temperature(lay person) if it helps someone’s intuition along.
Why is one definition more fundamental than another? Why is only one definition “actual”?
Because one is true in all circumstances and the other isn’t? What are you actually objecting to? That physical theories can be more fundamental than each other?
I admit that some definitions can be better than others. A whale lives underwater, but that’s about the only thing it has in common with a fish, and it has everything else in common with a whale. You could still make a word to mean “animal that lives underwater”. There are cases where where it lives is so important that that alone is sufficient to make a word for it. If you met someone who used the word “fish” to mean “animal that lives underwater”, and used it in contexts where it was clear what it meant (like among other people who also used it that way), you might be able to convince them to change their definition, but you’d need a better argument than “my definition is always true, whereas yours is only true in the special case that the fish is not a mammal”.
The distinction here goes deeper than calling a whale a fish (I do agree with the content of the linked essay).
If a layperson asks me what temperature is, I’ll say something like, “It has to do with how energetic something is” or even “something’s tendency to burn you”. But I would never say “It’s the average kinetic energy of the translational degrees of freedom of the system” because they don’t know what most of those words mean. That latter definition is almost always used in the context of, essentially, undergraduate problem sets as a convenient fiction for approximating the real temperature of monatomic ideal gases—which, again, is usually a stepping stone to the thermodynamic definition of temperature as a partial derivative of entropy.
Alternatively, we could just have temperature(lay person) and temperature(precise). I will always insist on temperature(precise) being the entropic definition. And I have no problem with people choosing whatever definition they want for temperature(lay person) if it helps someone’s intuition along.