Classical Surprise: -ㄴ/은/는고 (Is It That...?)

This grammar point functions as a sentence ending for questions. It specifically pairs with "Wh-questions" (who, what, where, when, why, how). In Middle Korean, there was a strict rule. You used -가 for Yes/No questions. You used -고 for questions with an interrogative word. Today, that distinction is mostly a stylistic choice. When you use -ㄴ/은/는고, you are usually talking to yourself or expressing a realization. It doesn't require a direct answer from someone else. It is like a thought bubble appearing over your head. You are pondering the nature of something. It attaches directly to the stem of verbs, adjectives, or the copula 이다 (to be). It changes slightly depending on whether you are describing a state or an action. It is like adding a vintage filter to your speech.

1. 1For Adjectives (Descriptive Verbs):
2. 2If the stem ends in a vowel, add -ㄴ고. Example: 크다 (to be big) becomes 큰고.
3. 3If the stem ends in a consonant, add -은고. Example: 좋다 (to be good) becomes 좋은고.
4. 4For Verbs (Action Verbs):
5. 5Add -는고 regardless of the final consonant. Example: 가다 (to go) becomes 가는고. Example: 먹다 (to eat) becomes 먹는고.
6. 6For Nouns (with 이다):
7. 7Add -인고. Example: 누구 (who) becomes 누구인고.
8. 8For Past Tense:
9. 9Add -었는고 or -았는고. Example: 어디 갔는고? (Where did they go?).

Use this when you want to sound poetic or dramatic. It is perfect for writing a diary entry where you question your life choices. You might use it when looking at a beautiful sunset and saying, "Why is it so red?" (어찌 이리 붉은고?). It is also common in specific regional dialects, like the Gyeongsang-do dialect, though the nuance is slightly different there. In modern Seoul, people use it mostly for humor or to mimic historical figures. If you are roleplaying a Joseon scholar, this is your go-to grammar. It is also great for reading classical Korean literature. It helps you feel the emotion of the author. Use it when you are genuinely impressed or puzzled by something grand. It turns a simple question into a moment of reflection.

Do not use this in a job interview. Your potential boss will think you are from the year 1750. Avoid using it with strangers at a convenience store. If you ask the clerk "How much is this?" using 얼마인고?, they might look for a hidden camera. It is not suitable for standard business emails or formal reports. It is too emotional and archaic for professional settings. Also, avoid using it for simple, mundane questions. Asking "Where is the bathroom?" with this grammar is like using a golden quill to write a grocery list. It is overkill. It is also not a "polite" ending in the modern sense. It belongs to the 해라체 (plain form) family, but with a dignified, old-fashioned twist.

One common mistake is forgetting the interrogative word. This grammar feels lonely without words like 누구 (who) or 무엇 (what). While not strictly forbidden now, it sounds most natural with them. Another mistake is mixing up the adjective and verb forms. Don't say 가는고 when you mean a state, or 좋는고 (which is just wrong). Remember that adjectives take -ㄴ/은고 and verbs take -는고. Yes, even native speakers mess this up when they try to sound fancy! Think of it like a grammar traffic light; you have to stop and check the word type before you go. Also, don't use it with high-politeness honorifics like -시- unless you really know what you're doing. It can get very confusing very fast.

Compare -ㄴ/은/는고 with -는가. Both are literary question endings. However, -는가 is more common in modern writing and feels like a standard "Is it...?" question. It is often used in newspapers or exams. In contrast, -는고 is much more archaic and emotional. It carries a sense of "I am amazed" or "I am deeply questioning this." Then there is -나요?, which is the soft, polite version used in daily life. If -나요? is a gentle breeze, -는고 is a gust of wind from a historical mountain. Finally, there is -느냐, which is a plain question ending used by elders to children. -는고 is more self-reflective and dignified than -느냐.