What are the grammatical roles of the two のs in the following sentence?

Question

What are the roles of the two の particles in the following sentence?

彼はこういうのがうまいのです。

Answer 1

彼はこういうのがうまいのです。

Sounds like you're confused about both の. Let's analyze.

Breaking it down

First, a literal word-by-word translation.

[彼]{"He"  }[は]{[TOPIC]  }[こう]{"like this"  }[いう]{"to say": verb  }[の]{[NOM]  }[が]{[SUBJECT]   }[うまい]{"good; skillful; tasty": adjective  }[の]{[NOM]  }[です]{"to be": verb}。

• いう is often used metaphorically, beyond its literal "to say" sense. This can be roughly similar to the English word "kind", which gets expanded in the phrase "kind of". Or English "like" meaning "similar to".
  While こういう literally means "saying like this", it's used more to mean "this kind, this kind of [something]", or "like this"
• The [NOM] marker above stands for "nominalizer". A nominalizer makes a "nominal" out of something, and a "nominal" is essentially a "noun" -- in this case, the noun is the preceding chunk.

The reason we need the first の is because we want to talk about a thing (the particle が can only work as a subject marker when it attaches to a noun), so we have to turn the verb いう into a thing.

The second の is a special kind of nominalizing: explanatory. In English, if you want to make an explanatory statement -- perhaps in response to a previous question, or in counter-response to someone's previous statement -- you'd use tone of voice, or a "because", or you'd just lay out the statement. In Japanese, you'd use the のです・のだ・んです・んだ construction (where ん is the casual contracted form of の).

The です or だ on the end just means "it is ... [whatever just came before]". The の here again acts as a nominalizer -- it makes a noun out of the entire preceding sentence.

Translating this directly gets a little clunky, but it's basically like saying in English, "it's that ... [whatever just came before]".

Putting it back together

The first の nominalizes the part before:

• 彼【かれ】はこういう
  "he ... like this"

This nominalized phrase, 彼【かれ】はこういう, is followed by the が subject particle. That's why I put the "..." in the middle there, because we see that the 彼【かれ】 is followed by は, the topic particle. Since this sentence has a が subject particle later, we can guess that the bulk of the details are about the subject, not the topic.

So we're talking about the subject, in relation to the topic. The subject is こういう, "like this", or as a nominalized phrase, "this kind of thing" (whatever it is, we don't know, but it must have been mentioned somewhere in the preceding context).

What are we saying about this subject? That it is うまい. (Note that うまい is broad: "good; good at, skillful; tasty" all work, depending on context.)

• 彼【かれ】はこういう[の]{●}がうまい
  He [TOPIC] this kind [NOM] good at
  ↓
  As for him, this kind is good at

Then we get that second の, as part of のです. Because we now know that this is an explanatory ending, we can guess that this is person A telling person B about person C:

• 彼【かれ】はこういう[の]{●}がうまい[の]{●}です
  He [TOPIC] this kind [NOM] good at [NOM] it is
  ↓
  It's that, for him, this kind is good at

The above is keeping things pretty literal to try to illustrate the Japanese grammar, but it's not very natural. Depending on context, there are various ways you might translate this into more sensible English.

• Ya know, these are the one's he's good at.
• He is good at this kind of thing.
  ... etc.