It's also worth remembering that "planet" is an ancient word that has changed its meaning over time. Originally "planet" was the name for bodies that were visible to the naked eye but too far from Earth to show a visible disk. If Earth had a moon that was much smaller, it likely would have been considered a "planet", back in the day.
With the advent of Galilean observations and Newtonian dynamics, "planet" came to mean "large body orbiting the sun", with asteroids being some object of indeterminate type (thus the weird name suggesting similarity to stars, not planets).
Concepts are made things. We divide reality up according to acts of selective attention based on what divisions are most useful to us. The way the world is, independently of us, constrains those divisions but does not determine them.
Most people are basically Platonists, and have a lot of trouble with this kind of epistemic pragmatism. Others--nominalists--reject the Platonic model with the claim that because categories are not determined by reality they must not be constrained by it.
Neither group has a good handle on how an apparently simple concept like planet can legitimately change over time while still being strongly constrained by objective reality as our knowledge expands and our purposes alter, but to an epistemic pragmatist it is precisely what you expect all concepts to do.
With the advent of Galilean observations and Newtonian dynamics, "planet" came to mean "large body orbiting the sun", with asteroids being some object of indeterminate type (thus the weird name suggesting similarity to stars, not planets).
Concepts are made things. We divide reality up according to acts of selective attention based on what divisions are most useful to us. The way the world is, independently of us, constrains those divisions but does not determine them.
Most people are basically Platonists, and have a lot of trouble with this kind of epistemic pragmatism. Others--nominalists--reject the Platonic model with the claim that because categories are not determined by reality they must not be constrained by it.
Neither group has a good handle on how an apparently simple concept like planet can legitimately change over time while still being strongly constrained by objective reality as our knowledge expands and our purposes alter, but to an epistemic pragmatist it is precisely what you expect all concepts to do.