You must look at how the word is used.
I like beer. (general category)
I had a beer. (specific)
We had a few beers last night. (plural general)
Of course beer and wood can be pural nouns.
That desk is constructed using many kinds of wood. (specific pieces of wood)
The woods are beautiful in the winter. (collection of trees)
Note: The definition of wood in the above sentences is not the same.
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