A fundamental thing: how we think about meaning. This boils down to how we think about rules and rule following.
One way to think about rules is an authority / submission model. When we want to know whether something is in accord with a rule, we look to a source of authority which answers the question. This is simple enough.
Consider rule-following paradoxes like 0, 2, 4, 6, … plus vs quus
Phlogiston vs oxygen
Negation of Classical logic vs negation of Intuitionistic logic
- We have a choice whether or not to consider them the ‘same’ negation