I wonder why you are so obsessed with this question. Even if there are some nouns which are invariably used countably or uncountably, it's still the case that there are plenty of others which are both, leaving us where? Leaving us with absolutely no "rule" that you can teach your students.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.
I don't understand what all this ado is about. I am just trying to figure out whether English has changed so much lately that countable nouns all of a sudden are allowed to be uncountable and vice versa.
Some of the native speakers here keep saying that, yes, that kind of metamorphosis is possible. I just want to know the truth.
But isn't it obvious that "bottle" is always countable or "window" is always countable?
5jj, please, don't get mad, buddy. Just prove it!
I think perhaps more examples are needed. I'll try to work on that.