Why does this sentence use 'ga arimasu' and not 'desu'?

I just finished that audio lesson (4.4), and I'm wondering the same.

I agree with what you've said. However... One of the results when searching "ninki" at romajidesu.com is "popularity." The word "popularity" is not the same as the word "popular"; the former is a noun and the latter is an adjective. (To note: "ninki can be used as a noun or adjective.)

So, even though in the audio course "desu" is actually spoken the first time, "arimasu" may well be correct as stated both when the sentence is later repeated and in the transcript.

Since "ninki" translates to the noun "popularity," I would assume that the line...
"Kare wa totemo ninki ga arimasu."
...could be translated to something like...
"He has much popularity."

This is what I've come up with, and hopefully it helps, but I'd definitely like further clarification as well.

Thanks. 

Thanks John - that does make sense when you put it that way! 
Cheers. It's pretty tough figuring it out for yourself sometimes. 
Ganbatte mimasho!

こんにちは (Konnichiwa) Andrew and JohnB232,

Thank you for your question!

JohnB232, you are absolutely correct! 

にんき (Ninki) is a tricky word. It's a noun, but sometimes it can look like an adjective! You can translate にんき (ninki) as "popularity" (a noun), but depending on the context, it can also mean "popular" (an adjective)! 

Andrew, you are 100% correct in saying that です (desu) means "is." It's also true that あります (arimasu) is used to show that something "exists." However, we can also use あります (arimasu) with the particle が (ga) to talk about something we "have." For example:

• ほん　が　あります。 (Hon ga arimasu.) "(I) have a book."

So, when we use にんき (ninki) with が　あります (ga arimasu), we can say something "has popularity": ie "(is) popular."

• かれ　は　とても　にんき　が　あります。 (Kare wa totemo ninki ga arimasu.) "He has lots of popularity. / He (is) very popular."

You can use にんき　です (ninki desu) and にんき　が　あります (ninki ga arimasu) interchangeably. However, にんき　が　あります (ninki ga arimasu) is more common in written Japanese, whereas にんき　です (ninki desu) is more common in spoken Japanese. 

I hope this helped! 

If you want to read a little bit more about the differences between です (desu) and が　あります (ga arimasu), you can check out these links:

です (desu)
https://members.rocketlanguages.com/members/japanese/lessons/5040/1-7-Introducing-Yourself

が　あります (ga arimasu)
https://members.rocketlanguages.com/members/japanese/lessons/5055/2-9-To-Be-and-To-Have

These are lessons from our brand new level 1 Language and Culture course, and explain everything in far more detail, so be sure to check them out!

Please let us know if you have any more questions.

べんきょう　を　がんばって　ください！ (Benkyō o ganbatte kudasai!)