For me the notion of domain is helpful in understanding OO. The definition of a domain is that everything inside it stands in determinate relations, whereas while multiple domains can interact they don't stand in determinate relations. Inheritance in classes, in adding more features to a class, can also have knock-on effects that interfere with the assumptions of other classes that are closely coupled to it, making classes an example of domain. Whole computers in a network are also domains; nodes can go down in which case no determinate expectations can be placed on them.
The existence of multiple domains is essentially postmodern as it creates, for practical purposes, multiple sources of truth. Because the expectations of one domain on another are weak, this naturally leads to a domain becoming robust against errors and inconsistencies from other domains, which leads to a stronger system. This type of robustness also helps components still be valid when they are placed into a different theory/environment that has additional properties. In some sense FP and OO are aiming at the same thing, that is making definitions that remain valid when the "arrows" of their environment change their meaning.
For a different perspective on this see Gerald Jay Sussman, "We Really Don't Know How to Compute!"
The existence of multiple domains is essentially postmodern as it creates, for practical purposes, multiple sources of truth. Because the expectations of one domain on another are weak, this naturally leads to a domain becoming robust against errors and inconsistencies from other domains, which leads to a stronger system. This type of robustness also helps components still be valid when they are placed into a different theory/environment that has additional properties. In some sense FP and OO are aiming at the same thing, that is making definitions that remain valid when the "arrows" of their environment change their meaning.
For a different perspective on this see Gerald Jay Sussman, "We Really Don't Know How to Compute!"