many修饰可数名词复数，如：There aremany people.
much修饰不可数名词复数，如：I have much money.
many作代词代表可数名词，如：Many of the students have great results.
much作代词代表不可数名词，如：Much of the air is fresh.
much还可以修饰动词，many不行。
如：I love you so much.
much还可以修饰比较级，many也不行。
如：He's much taller than her.
It's much more difficult than you thought.
