Choosing between many and much depends on what kind of noun you are talking about.
The word many is used to refer to a large number of things that can be counted, or nouns that have a plural form. This type of noun is called a count noun. Things like "cats," "books," "offices," and "friends" are plural count nouns. Below are some examples of many used with count nouns.
The word much is used to refer to a large amount of something that cannot be counted and does not have a plural form. This type of noun is called a noncount noun. Things like "milk," "air," "homework," and "luggage" are noncount nouns and do not have plural forms. (Click here for a list of more noncount nouns.) Below are some examples of much used with noncount nouns.
Just remember: if the noun has a plural form, use many. If it does not have a plural form, use much.
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