It is "code that changes together" but also an expression of which code depends on what and in what kind of manner does it do so (e.g. is one subsumed by the ot

It is "code that changes together" but also an expression of which code depends on what and in what kind of manner does it do so (e.g. is one subsumed by the other or is used by 3x other modules). Understanding where things live is also a statement on the composability of the code and how many assumptions about the outside world that the interfaces make. It's also worth noting that there's likely not one single "correct" organization/taxonomy, and certainly not one that's static and guaranteed to last forever. It truly is one of the most complex parts of programming because it's subjective, subject to change and is in a lot of ways right through the center of what it means to abstract something in the first place. I don't think there are any simple answers because it's equal parts philosophical and mundane. Software mixes things that model the real world, convenient fictions, abstract truths and guilty hacks and I believe trying to make sense of it is at least as much an art as a science.