Some words are generally considered as uncountable, but you can add “-s” or “-es”. When you do that, you change the meanings of those words. Here are a few examples:
water - waters
It is clear that “water” is uncountable, but when we talk about the water in the oceans, in the seas, we must add “-s”. So we say “sea waters”. Here is an example from the Bible – God said, “Let there be an expanse between the waters to separate water from water.” God was talking the waters in the ocean. He used its plural form.
wood – woods
“Wood” is material for furniture. It is uncountable. When we add “-s”, the meaning changes. “Woods” refers to trees and plants in a wooded area, a small forest.
glass – glasses
When we talk about window glass, “glass” is uncountable. However, in ” Would you like a glass of water?” “glass” is countable here. You can say: “Three glasses of water!” Here the meaning has already changed. The glass is the container of the drinking water. Another example is “a pair of glasses”. Here you must always use the plural form when you talk about the glasses you are wearing.
There are some other strange words. “Mail” is uncountable, but nowadays, we use “emails” all the time. “change” is countable. We say “many changes”. But when we talk about money: “Do you have some change?” The “change” is uncountable. You don’t say “Do you have some changes? (wrong)” We can “small talk”, but we don’t say “small talks”.
Some words are countable, but you never add “-s” even though you are using them as countable nouns. “Police” is such a word. You say “Police are coming!” Not “Police is coming!” (wrong). “Cattle” and “aircraft” are two other examples: ”Japanese aircraft were strong on maneuverability.” ”Cattle were inclined to remain in the territory.”
“People” is a countable noun, but you don’t need to add “-s”. When you add “-s”, it means peoples from different nations.
– Ron Lee