거든요 (explanatory) - Because You See, You Know

This pattern sits at the very end of your sentence. It replaces the standard -(아/어)요 ending. You use it when the listener asks "Why?" or even before they ask. It signals that you are about to provide the background reason for a situation. Imagine you are at a cafe and your friend asks why you aren't drinking coffee. You say, 잠을 못 잤거든요 (Because, you see, I couldn't sleep). The magic of 거든요 is that it assumes the listener doesn't know the reason yet. It’s like giving them a missing puzzle piece. It adds a layer of softness to your explanation. Without it, some reasons can sound a bit too blunt or even rude.

1. 1For Verbs and Adjectives in the present tense, just add 거든요 to the stem. It doesn't matter if the stem ends in a vowel or a consonant.
2. 2가다 (to go) → 가거든요
3. 3먹다 (to eat) → 먹거든요
4. 4예쁘다 (to be pretty) → 예쁘거든요
5. 5For Nouns, use (이)거든요.
6. 6If the noun ends in a consonant: 학생 + 이거든요 → 학생이거든요
7. 7If the noun ends in a vowel: 의사 + 거든요 → 의사거든요
8. 8For the Past Tense, attach it to the past tense stem (았/었/였).
9. 9했다 (did) → 했거든요
10. 10바빴다 (was busy) → 바빴거든요
11. 11For the Future Tense, use -(으)ㄹ 거거든요.
12. 12갈 것이다 (will go) → 갈 거거든요
13. 13할 것이다 (will do) → 할 거거든요

Use this when you want to be helpful and explanatory. It’s great for ordering food. If a waiter asks if you want more kimchi, you might say, "No thanks, 맵거든요" (Because, you see, it's spicy). It explains your choice.

In job interviews, it helps you elaborate on your skills. If they ask why you speak Spanish, you say, "멕시코에서 살았거든요" (You see, I lived in Mexico). It makes the conversation feel like a real dialogue rather than an interrogation.

When asking directions, if someone looks confused why you are asking, you can add, "길을 잃었거든요" (Because, you see, I'm lost). It builds empathy. Think of it like a grammar traffic light—it signals to the listener that an explanation is coming through, so they should pay attention to the "why."

Don't use 거든요 with your boss if they are angry at you. It can sound like you are making excuses. In very formal settings, like giving a speech or writing a report, stick to -기 때문에.

Also, avoid using it if the listener already knows the reason. If you both are standing in the rain and you say, "비가 오거든요," your friend might look at you like you have two heads. They can see the rain! In that case, you’d use -잖아요 instead.

Never use it to start a brand new topic out of nowhere. It needs a context or a previous statement to explain. Using it too much in one conversation can make you sound a bit defensive, like you're constantly justifying yourself. Yes, even native speakers mess this up sometimes, so don't sweat it too much!

One big mistake is mixing it up with -아/어서. While both give reasons, -아/어서 connects two clauses in one sentence. 거든요 usually ends the sentence.

• ✗ 비가 오거든요 우산을 가져가세요.
• ✓ 비가 오거든요. 그래서 우산을 가져가세요.

Another slip-up is using it with people much older than you in a way that sounds too casual. Even though it has the 요, the tone is quite intimate. If you use it with a grandparent you aren't close to, it might sound slightly impolite.

Lastly, don't use it for objective facts that everyone knows. "지구는 둥글거든요" (Because, you see, the earth is round) sounds like you are talking down to someone. Keep it for personal reasons or specific info the other person lacks.

How is it different from -잖아요? This is the most common point of confusion. Use 거든요 when the listener doesn't know the reason. Use -잖아요 when the listener already knows or should know the reason. It’s like saying "As you know..."

What about -(으)니까? This one is more about a logical basis for a command or suggestion. "Since it's raining, let's stay home." 거든요 is purely for providing background info to explain a state or action.

Think of -기 때문에 as the "textbook" reason. It's formal and cold. 거든요 is the "coffee shop" reason. It’s warm, conversational, and a bit more personal. It’s like the difference between a legal document and a text message from a buddy.