거든 (conditional) - If/When (Casual)

At its heart, 거든 creates a conditional sentence. It translates roughly to "if" or "when" in English. However, it has a very specific vibe. It implies that once the condition in the first clause is met, the second clause should follow immediately. Most of the time, the second part of your sentence will be a command (-세요), a suggestion (-(으)ㄹ까요), or a statement of intent (-(으)ㄹ게요). You are basically saying, "Hey, if this happens, do this!" It’s a very dynamic grammar point. It’s not about abstract theories. It’s about real life happening in real time. If you use it correctly, you'll sound much more natural and less like a recorded textbook.

1. 1Getting 거든 onto your verbs is actually pretty simple. It doesn't care if there's a final consonant or not. It's one of the friendlier grammar rules in that regard.
2. 2For present tense verbs and adjectives: Just take the stem and add 거든.
3. 3가다 (to go) becomes 가거든.
4. 4먹다 (to eat) becomes 먹거든.
5. 5바쁘다 (to be busy) becomes 바쁘거든.
6. 6For past tense: Use the past tense stem (-았/었) and add 거든.
7. 7왔다 (came) becomes 왔거든.
8. 8읽었다 (read) becomes 읽었거든.
9. 9For nouns: Use -(이)거든.
10. 10학생 (student) becomes 학생이거든.
11. 11친구 (friend) becomes 친구거든.
12. 12It’s like building with LEGO blocks. Once you have the stem, you just snap the 거든 on top. Even irregular verbs behave relatively well here. For example, 듣다 (to hear) changes to 들으시거든 in honorifics, but in casual speech, you might just hear 듣거든. Just remember: Stem + 거든 = Conditional Action.

This is where 거든 shines. Use it when you are giving someone a "Plan B" or an instruction.

• Ordering Food: Imagine you're at a cafe. You could say, 자리가 없거든 다른 데로 가자 ("If there are no seats, let's go somewhere else"). You are setting a condition and immediately offering a solution.
• Asking Directions: You're helping someone find a subway station. 우체국이 보이거든 왼쪽으로 도세요 ("If the post office appears, please turn left"). It acts as a trigger for the next step.
• Job Contexts: A coworker is leaving for a meeting. 회의가 끝나거든 연락 주세요 ("When/If the meeting ends, please contact me"). It’s professional yet direct.
• Promises and Intent: If you want to tell your partner you'll help, 도움이 필요하거든 말해 줘 ("If you need help, tell me").

It’s the go-to choice for "If/When" in spoken Korean when the listener needs to do something. It’s practical, efficient, and honestly, a bit of a time-saver.

Every grammar rule has its boundaries. You shouldn't use 거든 for general truths or scientific facts. For example, don't say "If you heat water, it boils" using 거든. That sounds weirdly like you're commanding the water to boil! Use -면 for that.

Also, avoid using 거든 in the second clause if it's just a simple observation. You can't say, 비가 오거든 기분이 좋아요 ("If it rains, I feel good"). That’s a no-go. Why? Because 거든 is an action-seeker. It wants a command or a suggestion. If you're just sharing your feelings, stick with -면.

Lastly, be careful with the tone. Since it's often used for commands, it can sound a bit strong if used with someone much older or in a very formal setting. Stick to -면 or -(으)시거든 if you're trying to be extra polite. Think of it like a grammar traffic light—green for friends and coworkers, but maybe a cautious yellow for your boss's boss.

One big trap is using the wrong ending in the second half of the sentence. Remember: 거든 loves imperatives! A common mistake is saying something like 배가 고프거든 밥을 먹어요. While not strictly "illegal," it sounds much more natural to say 배가 고프거든 밥을 먹으세요 or 먹자.

Another mistake is forgetting that 거든 can also mean "Because..." at the end of a sentence. This can get confusing! If you hear someone say 어제 바빴거든, they aren't setting an "if" condition. They are explaining why they didn't call you. Don't worry, even native speakers mess this up sometimes, or rather, the context usually clears it up.

Also, don't overcomplicate the stem. Some learners try to add too many bells and whistles. Keep it simple. Verb stem + 거든. No need for extra particles in the middle. If you find yourself sweating over the spelling, you might be overthinking it.

The biggest rival is -면.

• -면: The generalist. Use it for anything. General truths, simple conditions, whatever. It’s safe. It’s like a plain cheese pizza. Everyone likes it, it works everywhere.
• 거든: The specialist. It's for conditional *actions*. It’s like a spicy pepperoni pizza. It’s got a specific kick and you use it when you want to get something done.

If you use -면, you're just saying "If A, then B." If you use 거든, you're saying "If A happens, I want you to do B" or "I will do B."

Another one is -(으)려면. That one specifically means "If you *intend* to..." whereas 거든 is more about the situation happening. For example, 공부하거든 is "if you happen to be studying," while 공부하려면 is "if you want/intend to study."