Dear all: First of all, I should announce that I am talking about it formally. I am just telling my understand about that. Some of them haven't been read in grammar books by me. So they may be wrong. English nouns can be divided into countable nouns and uncoutabel nouns. The following are usually uncountable nouns: 1. Liquid. Such as water, wine, milk and so on. 2. Very fine,multitudinous things. Such as rice, hair, dirt, and so on. 3. Nubbly and sheet like things. Such as motton, meat, bread, paper and so on. These uncountable nouns have no plural forms. So we can't add an "s" behind them. Some words can be countable nouns, and uncountalbe nouns as well. It depends on the meaning of them. For example, orange, if it refers to a kind of fruit, it's a countable noun, and if it refer to the kinds of juice, it's an uncountable noun. When chicken means the kind of animal, it's a countable noun,and it's an uncountable noun when it means a kind of meat. "Cabbage" is countable noun when it is growing in the fields or selling in a supermarket.But after it is cooked and put in a dish, it's uncountbale.Do sports means you do different kinds of sports, while "do sport" emphasize the quantity of the sport. It's the same case with “drink" and "drinks", "fruit" and "fruits".About "vocabulary" and "vocabularies", I personally think vocabulary is the number of the words you know, and "vocabularies" means words.And fish may be the most troublesome one. In my mind, "fish" is an uncountable noun when it means fish meat. When it refers to the kind of animal, when you try to mention its number, its single form is the same as its plural form, just like sheep, deer,and so on. If we mean to talk about the kinds, we should say fishes. Then my ideas about paper, paper is a countable noun, but newspaper, tablepaper, and testpaper are countable nouns. It seems that some nouns are irreasonable. For example, news is an uncountable noun, while message is a countable noun. I don't think they are irreasonable. What is grammar? It's the ususl rule of a kind of language. Usual doesn't mean all. And we don't creat a language according to grammar. So, language is more of chronic. Many new words come into being every year. Just imagine, before a new word appears, will someone just write down all the rulers of using it? Of course not. One uses it like this, then others follow, then the grammar established by usage. Some one says, the most important thing is what we say should make sense, yes, I agree. I had write the same idea in one of my posts. But I only mean in daily communicating. But in some formal articles, we must pay attention to the grammar. For I have just finished a rather long and dull article. So my mind may be not so clear. I hope I didn't make too many mistakes in it.:-) And if I remember more about the plural forms, I will write down later. And I am waiting for the free Peking duck.Leslie.