在英文中，名词是可数还是不可数，都会决定前面该用哪个限定词，也会决定后面的动词型态，因此务必要区分名词是可数还是不可数。
可数名词
可数名词可以用数字来计算。这种名词有单数和复数形；单数形的限定词可以用 a 或 an。如果要询问某个可数名词的数量有多少，可以用「How many?」来问，再搭配可数名词的复数形。
单数
复数
one dog
two dogs
one horse
two horses
one man
two men
one idea
two ideas
one shop
two shops
例句
She has three dogs.
I own a house.
I would like two books please.
How many friends do you have?
不可数名词
不可数名词无法用数字来计算。这类名词可能是抽象的概念，或者太小丶非固态的物体（液体丶粉状物丶气体等）。不可数名词会使用动词单数形，通常没有复数形。
举例
tea
sugar
water
air
rice
knowledge
beauty
anger
fear
love
money
research
safety
evidence
我们不能在不可数名词前面加 a 或 an，如要表达它的数量，就得用 some丶a lot of丶much丶a bit of丶a great deal of 之类的量词来表达，要更确切的话还可以用 a cup of丶a bag of丶1kg of丶1L of丶a handful of丶a pinch of丶an hour of丶a day of 等量词或测量单位。如果想询问数量，可以用「How much...?」来问。
例句
There has been a lot of research into the causes of this disease.
He gave me a great deal of advice before my interview.
Can you give me some information about uncountable nouns?
He did not have much sugar left.
Measure 1 cup of water, 300g of flour, and 1 teaspoon of salt.
How much rice do you want?
微妙之处
有些名词在别的语言中可数，但在英语中却不可数，因此得遵循不可数名词的规则。这类名词最常见的有：
accommodation, advice, baggage, behavior, bread, furniture, information, luggage, news, progress, traffic, travel, trouble, weather, work
例句
I would like to give you some advice.
How much bread should I bring?
I didn't make much progress today.
This looks like a lot of trouble to me.
We did an hour of work yesterday.
要特别留意的是 hair 这个名词，在英语中一般是不可数的，因此通常不会用复数形，只有在特指单根头发时才会是可数名词。
例句
She has long blond hair.
The child's hair was curly.
I washed my hair yesterday.
My father is getting a few grey hairs now.（指的是一根根的头发）
I found a hair in my soup!（指的是单根的头发）