-- in normal usage the first reaction of most listeners.readers when they hear The object exists in space and time is to ask "Which object?"
--- My reaction would be the same.
With plural objects, we know that all objects are being discussed.
---Me, too.
Crerture, like object is too non-specific a word in normal language. Our first reaction is to ask "Which creature?" We don't have that problem with plural creatures.
--Me , too.
I've agreed in this thread with native teachers' explanations. I'm of the same opinion as yours. However, that's not what I'm asking.
I know well that "the creature" and "the object" as a generalized concept don't make sense, while "the lion" and "the computer" do.
What I'd like to ask is why the former 2 aren't OK, while the latter 2 are.
What should I answer if my students in Japan ask me the above question?
If I answered what you said above, my students wouldn't accept. I have to say that's the way native speakers do, and their ideas are valid with native people with the same linguistic experience, though not with people without such experience.
I myself have some extent of experience of that kind. I've been teaching English for about 40 years. I've accepted native speakers' linguistic conventions as necessary.
However, I can't put, in a short time, years of experience into my students' minds.
Probably I won't be able to convince you native teachers. You only have to teach to the students with years of experience, who cannot live on without such experiences.
I know well that I'm asking you native teachers something very stressful, which you've never thought of. So in fact I don't expect so much of you.
But if you are kindly to consider this matter, I'd like your opinions. Probably you would be frustrated by my seemingly unanswerable question. But teachers who have experienced teaching in other countries, or who are now teaching students in your country without years of experience might understand me.
Here I'll state again my opinion in my reply to probus (I changed a bit.)
Native speakers make appropriate choices as to which article to take based on linguistic conventions. Almost everyone makes an appropriate choice, but what on earth makes it possible? Probably they, when choosing articles by experience, share the identical psychological tendency. Because each person's psychological tendency is the same, there should be in it reasonability which humans are born with.
So I'd like to consider this matter in terms of reasonability.
Countable nouns which cannot be used as a generalized concept are, I suppose, a creature and an object, while the other countable nouns can be used as such. Among the latter countable nouns the species names (the lion, the oak ---) are often used.
So why a creature and an object aren't used as such?
You say it's because the creature and the object are usually considered as a specific one, not a conceptual one.
Why then does there arise such an misunderstanding? It's because you can't use them as a generalized concept. That's a convention. So how was such a convention got by people?
I surmise there was a psychological tendency that people didn't want to use them as such. I surmise people long ago are interested in categorization, and a lion and an oak seemed easy to be categorized, while an object and a creature not.
That's just my surmise, but it seems somewhat reasonable.
As aforesaid, it's reasonability that matters, not rightness. My idea seems at least to me as practical in teaching sites.
I'd like your opinions if you like.