What's the difference between mnoho and hodně? Or are they interchangeable?
Mnoho expresses quantity and sounds quite formal, while hodně or moc expresses not only quantity, but also intensity.
To give an example:
you can say "Jím hodně." or "Jím mnoho." because this sentence is about quantity. (Althought "Jím mnoho." is technically correct, it doesn't really sound natural, so I wouldn't recomend using it in this case.)
you can say e.g. "Je hodně smutný./Je moc smutný." ("He is very sad.") but you cannot say "Je mnoho smutný." because this is about intensity. We use "velmi" instead.
So mnoho would be translated as "a lot", while hodně can be both "a lot " and "very"? And hodně can be used to replace mnoho, but not the other way around, right ?
Correct! There is also the aspect of "mnoho" being more formal and "hodně" more casual in spoken language.