The main difference between countable and uncountable nouns is simple. Countable nouns can have a number or an indefinite article (a/an) assigned to them, whereas uncountable nouns cannot:
There’s also something else to consider. Only some countable nouns can use particular determiners (many, few, some):
A few cups some people many desks
Whereas only uncountable nouns can use other determiners (much, little):
A little water How much rubbish is there? A little information
As you can see then, nouns come in different shapes and sizes.
There are some tricky concepts to understand for students, though, and one of them is this: it isn’t always obvious which nouns are countable and which aren’t. To complicate it further, two words could also have similar meanings but one could be countable and the other uncountable.
Take the following, for example:
Both are referring to lightning, but lightning is describing the weather lightning, whereas the strike of lightning is talking about a particular strike that happens. They are obviously similar but also very different.
Another issue is that sometimes an uncountable noun of material (rice, iron ore, steel, wine etc) can be changed into a countable noun if we are talking about different flavours or uses of the item:
We’ve got a huge selection of steel
There is a wide variety of rice available in the store
And similarly, when we are ordering drinks, uncountable nouns can turn into countable nouns:
"I’d like two wines please, this one and this one"
"3 waters for the table will be enough"
To complicate things further, some abstract nouns (life, experience, idea, honour, beauty etc.) can be countable in one piece of speech, but uncountable in another:
Life is a struggle (uncountable) His experience speaks for itself (uncountable)
Get a life (countable) What an experience that was (countable)
Because of all the different ways nouns can be used, it’s really important to encourage your students to have a dictionary so they can check how to use them.