There was a Soviet philosopher, Evald Ilyenkov, whose books taught me about a "minimal working model". I'll explain it in my own words.

People do not think with words: people think with things. Words serve merely as pointers to things. Some things are easy to point at; Ilyenkov talks about a cow. Some things are much harder to point at; Ilyenkov, being a Marxist, wanted to point to private property, we need to point to an object. Usually we try to talk about them using definitions, that is some sequences of words that are supposed to describe a thing. Such discussions are notoriously unproductive. The reason is that words are not really good as pointers: we have much more things than we have words and we have to reuse the same words to point to different things in different contexts. Yet in a phrase words look same so we tend to conflate these different things. As a result we get lost and go around in circles.

So instead of definitions Ilyenkov talks about a notion. Notion is something that reliably points to a thing that is hard to point at. It does not have to be an abstract thing: for example, we cannot point to radio. We can point to a household radio apparat but it has way too many parts completely unrelated to radio as a principle. So instead we build a minimal radio that has like three or four parts yet is capable of emitting or receiving radio waves.

We can do the same with abstract things too using the same approach. Let's build a minimal working model of a thing. "Working" so that the model indeed has the quality we are after; and "minimal" so that if we lose a single part, the quality is gone. Since the thing is abstract the model will also be abstract, that is it will be a sequence of words too, very much like a definition, but not quite.

(The same principle is widely used in parables: they describe some situation and thus try to guide your attention to certain qualities of it, hoping to trigger understanding. Sometimes it is hard to even name the thing they are pointing at, yet their pointing power is palpable. I myself often think about the parable about seven blind people and an elephant. You see I'm not naming the thing it points at: I don't have a good name for it.)

So let's go back to object oriented programming. What would be a minimal working thing that we can reliably call an object?

Here is what cannot be there. First, there must be no inheritance. If inheritance were required, then the first thing we build wouldn't be an object as it would have nothing to inherit from. Only the second thing would be an object and only because it inherited from the first. But this does not seem right. Second, there must be no polymorphism on the same grounds.

But at the same time if we do this:

    class Aaaa
        method bbbb():
            ...

then it is too minimal. It is hard to say how it is different from a function. It is not an object at all. Yet; there is a missing part that would turn this into a true object, but what the part is could be somewhat surprising.