Much - Many - A Lot Of

All the three words refer to quantity. However, usage varies according to the type of statement and nouns. The following table is the summary.

For example:

•    They have a lot of money.

(“Money” is uncountable noun, and it is in the affirmative statement; therefore, “a lot of” can be used.)

•    I don’t have much/a lot of money.

(“Money” is uncountable noun, and it is in the negative statement; therefore, either “a lot of” or “much” can be used.)

•    There are many/a lot of students in class.

(“Student” is countable noun, and it is in the affirmative statement; therefore, either “many” or “a lot of” can be used.)

•    There aren’t many/a lot of students in class. (“Student” is countable noun, and it is in the negative statement; therefore, either “many” or “a lot of” can be used.)