I suppose it's subjective (i.e. it's something which we must use our intelligence to decide, machine-like rules can't decide that for us), and so it's something we vote on.
As you know, as a moderator I usually avoid voting to close a question (because my vote isn't a "vote", it's binding), but I will close topic I see as duplicates (and people don't usually complain when I do).
However there are many topics on the site and I don't remember every one: if I don't vote that doesn't mean it's not a duplicate, it may just mean that I haven't noticed that there is a duplicate.
And so I recommend that you vote to close topics which you consider to be duplicates.
In general I'd suggest that topics are identical if they have exactly the same answer ... if one question asks something different then it deserves a different answer, so if they don't deserve different answers maybe they're asking the same thing.
I (personally) don't like to see copy-and-pasted answers (exactly the same answer in more than one topic).
The SE software raises a moderator flag when an answer is copy-and-pasted, so I suppose that SE too doesn't like or is suspicious of copy-and-pasted answers.
Instead of copy-and-pasting an answer it might be better to vote-to-close as duplicate (if you think it is a duplicate); or, post a "see also" comment (if you think it's not quite a duplicate, but so closely related that the OP would be interested in reading an answer that was posted in reply to the previous topic).
This isn't a duplicate IMO:
- Why do planets form into spherical objects? vs
- Why do soap bubbles form spherical objects?
They actually have different answers (the first is caused by "gravity" and the second is caused by "surface tension", though both are caused by "minimizing potential energy" or something like that).
On the other had I just closed one of the following two questions as a duplicate:
Does the level of awareness of an awakened buddhist also stay the
same event when he
But when an enlightened person lives he could be in the present all
the time. But when you sleep your conscious/awareness may be different
or just disappear.
So does the level of awareness of an enlightened person also change or
stay the same even when sleeping.
Do Arhats sleep?
I have read somewhere that Arhats (people who attained Nirvana) do not
sleep like normal people do. Instead they just stay calm in a suitable
position to give the rest required for the physical body, but their
mind is always alert...
Is this true?
I dont see anything that one is asking which the other isn't already asking, furthermore one attracted exactly the same answer as the other.
Conversely, these aren't exact duplicates:
Please read this Help topic: Why are some questions marked as duplicate?