上級の「〜だけでなく...も」 (-거니와)

1. 1Thematic Parallelism: The two connected clauses must share the same positive or negative sentiment. -거니와 is used for accumulation, not contrast. You stack a positive fact upon another positive fact, or a negative upon a negative. Combining a positive and a negative clause with -거니와 creates a logical dissonance that sounds unnatural to native speakers. For contrast, you would use a different connector like -지만 or -(으)나.

• Correct (Positive + Positive): 그 배우는 연기력이 뛰어나거니와 인품도 훌륭하다. (That actor not only has outstanding acting skills, but his character is also excellent.)
• Correct (Negative + Negative): 이 기계는 오래되었거니와 고장도 잦다. (This machine is not only old, but it also breaks down frequently.)

1. 1Inclusion of an Additive Particle: To complete the but also meaning, the second clause almost invariably contains an additive particle like ~도 (also, too) attached to the subject or object, or an adverb like 또한 (furthermore, moreover) at the beginning of the clause. While not a 100% rigid grammatical rule, its omission is rare and can weaken the intended cumulative effect. The particle 도 is the essential glue that solidifies the additive relationship between the two clauses.

Almost never in casual, spontaneous conversation. Its use is limited to prepared, formal speech: academic presentations, news broadcasts, official ceremonies, and perhaps debates. In 99% of spoken situations, -(으)ㄹ 뿐만 아니라 or -고 is the more natural and appropriate choice.

This is a key distinction. While both add information, they have different nuances.

• -거니와 connects two parallel facts of similar status or weight. It presents them as two existing truths that complement each other. Think of it as Fact A + Fact B.
• -는 데다가 implies piling on. It suggests that the second clause is an additional item being stacked *on top of* the first, often making a situation more extreme. Think of it as On top of Fact A, there's also Fact B. It often carries a nuance of “to make matters even better/worse.”
• Example: 그 식당은 음식이 맛있거니와 경치도 좋다. (The restaurant's food is tasty, and the view is also good.) — Parallel qualities.
• Example: 주말이라 길이 막히는 데다가 비까지 와서 운전하기 힘들었다. (Because it was the weekend the roads were jammed, and on top of that, it was even raining, so driving was difficult.) — Piling on negative conditions.

Absolutely. The rule is about thematic parallelism, not positivity. As long as both clauses express a negative or undesirable quality, the structure works perfectly.

• 그 방은 월세가 비싸거니와 교통도 불편해서 인기가 없다. (That room not only has expensive monthly rent, but the transportation is also inconvenient, so it's not popular.)

While not a textbook rule that makes its omission grammatically incorrect, its presence is overwhelmingly standard in natural usage. Omitting 도 (or 또한) can make the sentence feel incomplete or less emphatic. It is the particle that truly solidifies the “also” part of the meaning, so it is highly recommended to always include it.

Its etymology helps explain its meaning. -거니와 is a fusion of older grammatical elements. It's related to the connective -거늘, which sets up a known fact or background situation, combined with the particle 와/과 (with, and). This origin story reinforces its modern function: acknowledging a given situation (-거늘) and adding something to it (-와).