© Tobias Woelke 2021
Sehr is an adverb and is indeclinable, ist means “very”. Viel can be used as an adjective or as an adverb and it means “many”.
Ich fühle mich sehr gut = I feel very well. .
Wir haben viele Haustiere = We have many pets.
Sehr is also used before the positive degree, while viel is used before the comparative.
Der Film war sehr interessant…. aber das Buch davon ist viel interessanter= The film was very interesting but the book about is much more interesting.
It is also correct to use both adverbs at the same time, e.g. “Ich brauche sehr viel Geld”, meaning that you need a lot of money.
Another example would be: Es gibt sehr viele Leute da.
I admit that it is a bit confusing, but German is also a matter of getting your ear used to certain rules that come by default and have no logical explanation.
Antonio ist sehr krank(Antonio is very sick)
Antonio ist sehr reich(Antonio is very rich)
Antonio hat eine kleine Wohnung(Antonio has a small flat)
Here we can see that sehr always comes before the adjective, although there are a few exceptions sehr always accompanies an adjective.
Peter hat viel Geld(Peter has a lot of money)
Peter hat viele Häuser(Peter has many houses)
Es macht mir viel Spass(I have a lot of fun)
With a few exceptions, viel always accompanies a noun.
NOTE: There are other cases where viel and mehr can be used together, which is equivalent to “much more”.
Peter hat viel mehr Geld als Klaus(peter has much more money than Klaus)
In this link you can read more about the differences of some words: