Learn Hardcore Japanese: kono resutoran ha azi dake de naku, ryouri no situ mo ii desu. - At this restaurant, not only the taste but also the quality of the food is good.

このレストランは = As for this restaurant, / Speaking of this restaurant, …
The real grammatical subject inside the sentence is often marked by が, but in this sentence it’s omitted:
- (このレストランは) 味だけでなく、料理の質もいいです。
- You could think of an underlying structure like:
  - 味がいいです。
  - 料理の質もいいです。

So は sets このレストラン as the thing you’re talking about, and then you make statements about its taste and the quality of its dishes.

How is 味だけでなく working grammatically, and what does each part mean?

味だけでなく breaks down like this:

味 – taste, flavor
だけ – only
で – the て-form of the copula だ (similar to and / being)
なく – adverbial form of ない (the negative)

Put together, AだけでなくB means “not only A but also B.”

So:

味だけでなく、料理の質もいいです。
- Not only the taste is good, but the quality of the dishes is also good.

The pattern you can remember is:

A だけでなく、B も … = Not only A, but B also …

I often see だけじゃなく or だけではなく. How do these differ from だけでなく?

They are very close in meaning; all express “not only A but also B”. The differences are mostly in formality and nuance:

だけでなく
- Neutral and standard.
- Common in writing and speech.
だけではなく
- Slightly more formal/polite feeling.
- は adds a stronger contrast: “not just A (at least), but also B.”
だけじゃなく
- Casual, spoken form.
- じゃ is the colloquial contraction of では.

In this sentence you could say:

このレストランは味だけでなく、料理の質もいいです。
このレストランは味だけではなく、料理の質もいいです。

Both are fine; the second feels a bit more emphatic or formal.

Why is だけ placed after 味? Could we put it somewhere else?

だけ always comes after the thing it limits.

味だけ = only the taste
料理の質だけ = only the quality of the dishes

In the pattern AだけでなくBも, A is the thing that だけ attaches to:

味だけでなく = not only the taste
料理の質だけでなく = not only the quality of the dishes

You cannot move だけ freely:

✔ 味だけでなく
✘ だけ味でなく (incorrect)

What exactly does 料理の質 mean? How is it different from just 質 or from 品質?

料理 – dishes, cuisine, food prepared at the restaurant
の – links the two nouns (like of in English)
質 – quality (general)

So 料理の質 = the quality of the dishes / the quality of the food (they serve).

Compared with:

質 alone – just quality, very general; you’d normally specify what:
- この店は質がいい feels incomplete; listeners expect 質 of what?
品質（ひんしつ） – more like product quality, often used in manufacturing, products, merchandise.
- 料理の品質 is understandable but sounds more like talking about a product spec; 料理の質 is more natural here.

What is the role of の in 料理の質?

の here is a possessive / attributive particle, similar to English of or the apostrophe ’s.

料理の質
- literally quality of the dishes
- or the dishes’ quality

Structure:

[Noun A] の [Noun B] → B that is related to A / B of A
- 日本の料理 – Japanese food
- 車の色 – the color of the car
- 料理の質 – the quality of the dishes

Why is も used in 料理の質もいいです? Could we use が instead?

も means also / too, and it matches the pattern AだけでなくBも.

味だけでなく、料理の質もいいです。
- Not only the taste is good, but the quality is also good.

Using が:

味だけでなく、料理の質がいいです。
- This is grammatically okay, but you lose the clear “A and also B” pattern.
- It can sound more like:
  - (It’s) not just about the taste; the (main point is that) quality is good.

So in not only A but also B, B is normally followed by も.

Why do we say いいです at the end? What’s the difference between いい, よい, and いいです?

よい – the original, more formal/basic form.
いい – the common spoken form; in most modern contexts this is what you use.
- Conjugations (past, negative) are still based on よい:
  - よかった (was good), よくない (not good).

Politeness:

いい – plain form (informal).
いいです – polite form (adding です).

So:

料理の質もいい。 – casual.
料理の質もいいです。 – polite (used in this sentence).

よいです is also correct but can sound a bit stiffer or written-formal in everyday speech.

Can I change the word order, like putting 味だけでなく at the beginning?

Yes, Japanese word order is fairly flexible with topics and adverbial phrases. For example:

味だけでなく、このレストランは料理の質もいいです。

This is grammatically fine and understandable. However:

The original このレストランは味だけでなく、料理の質もいいです。
starts with the restaurant as the topic, which sounds very natural when introducing or reviewing the restaurant.

Both are correct; the original is more typical for this kind of sentence.

Could we express the same idea with も on both parts, like 味も料理の質もいいです? How does that differ?

Yes:

このレストランは味も料理の質もいいです。

This means:

This restaurant has both good taste and good dish quality.

Difference in nuance:

味だけでなく、料理の質もいいです。
- Emphasizes “not only A but also B.”
- Often used when someone might expect only A to be good, and you add B as a nice extra.
味も料理の質もいいです。
- Puts 味 and 料理の質 on equal footing from the start.
- Feels more like a simple listing: both A and B are good.

So the original sentence carries a “not only … but also …” contrast that AもBも lacks.

Could we say このレストランの味は instead of このレストランは味? What changes?

Yes, you can say:

このレストランの味は、料理の質もいいです。
(though you’d probably rephrase the rest for naturalness)

But in general:

このレストランは味だけでなく…
- Topic: this restaurant
- Then we talk about multiple aspects of it (taste, quality).
このレストランの味は…
- Topic: the taste of this restaurant
- You are now focused specifically on the taste, not the whole restaurant.

Because the sentence evaluates two different aspects (taste & quality of dishes), it’s more natural to make このレストラン the topic, as in the original.

What exactly is でなく grammatically? Is it just で + ない?

でなく comes from the copula だ in its て-form plus the negative ない:

だ (copula) → で (its て-form)
ない (negative) → なく (adverbial form)

So:

だ → で
で + は + ない → ではない (is not)
Adverbial/conjunctive form → ではなく

When you drop は (especially in だけでなく), you get:

だけではなく → だけでなく

Functionally, you can just remember:

A だけでなく B も = not only A but also B

and not worry too much about the internal derivation unless you’re into grammar details.