> So when X is a model of Y, then Y is always also a model of X? Yes. > That seems like a strange definition of “model”. Yes, it does, but I can defend it.

> So when X is a model of Y, then Y is always also a model of X? Yes. > That seems like a strange definition of “model”. Yes, it does, but I can defend it. It's analogous to the definition of "information". If a system X contains information about a system Y then it is always the case that Y also contains the same amount of information about X. The distinction between "model" and "modeled" is purely artificial in the most literal sense: the thing we generally label "model" is the thing we humans made.