15. Korean Grammar: 아/어서, (으)니까, 때문에 (Expressing Reasons)

Korean Grammar: 아/어서, (으)니까, 때문에 (Expressing Reasons)

In today’s lesson, we’ll learn how to express reasons and causes in Korean using 아/어서, (으)니까, and 때문에. These grammar points are used to explain why something happens, but they each have their own nuance.

Let’s dive in! 🚀

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1. 아/어서 (Because/So)

아/어서 connects two actions or reasons, similar to "because" or "so" in English.

🔹 Sentence Structure:

👉 Verb/Adjective Stem + 아/어서

• Use 아서 if the last vowel is ㅏ or ㅗ.
• Use 어서 if the last vowel is anything else.

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🔸 Examples with Illness and Symptoms (질병과 증상)

Example Sentence Translation

머리가 아파서 병원에 갔어요.	Because I have a headache, I went to the hospital.
감기에 걸려서 집에 있었어요.	I stayed home because I caught a cold.
열이 나서 학교에 못 갔어요.	I couldn’t go to school because I had a fever.
피곤해서 일찍 잤어요.	I slept early because I was tired.
배가 아파서 약을 먹었어요.	I took medicine because my stomach hurt.

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2. (으)니까 (Since/Because)

(으)니까 is used to explain a reason but often emphasizes personal opinion, advice, or commands. It feels a bit more subjective than 아/어서.

🔹 Sentence Structure:

👉 Verb/Adjective Stem + (으)니까

• If the verb stem ends in a consonant, use 으니까.
• If the verb stem ends in a vowel, use 니까.

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🔸 Examples with Illness and Symptoms

Example Sentence Translation

감기에 걸렸으니까 쉬세요.	Since you have a cold, take a rest.
열이 나니까 병원에 가세요.	Since you have a fever, go to the hospital.
피곤하니까 일찍 자요.	Since you're tired, sleep early.
배가 아프니까 약을 드세요.	Since your stomach hurts, take some medicine.
기침하니까 물을 마셔요.	Since you're coughing, drink some water.

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3. 때문에 (Because of)

때문에 is used to indicate that something happened because of a specific reason or noun.

🔹 Sentence Structure:

👉 Noun + 때문에
👉 Verb + 기 때문에 (for verb reasons)

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🔸 Examples with Illness and Symptoms

Example Sentence Translation

감기 때문에 학교에 못 갔어요.	I couldn’t go to school because of a cold.
두통 때문에 일하기 힘들어요.	It's hard to work because of a headache.
열 때문에 병원에 갔어요.	I went to the hospital because of a fever.
피로 때문에 쉬고 있어요.	I’m resting because of fatigue.
기침 때문에 목이 아파요.	My throat hurts because of coughing.

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4. What’s the Difference? 🤔

Grammar Meaning Usage Example

아/어서	Because/So	Shows cause-effect naturally, can’t be used with commands or suggestions.	배가 아파서 병원에 갔어요. (I went to the hospital because my stomach hurt.)
(으)니까	Since/Because	Used for personal opinions, suggestions, or commands.	배가 아프니까 병원에 가세요. (Since your stomach hurts, go to the hospital.)
때문에	Because of	Used with nouns (or verbs with -기 때문에). More formal and direct.	배 아픔 때문에 병원에 갔어요. (I went to the hospital because of stomach pain.)

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5. Useful Vocabulary (Illness & Symptoms)

🔹 Illness (질병)

Korean English

감기	Cold
독감	Flu
두통	Headache
복통	Stomachache
피로	Fatigue
열	Fever

🔹 Symptoms (증상)

Korean English

기침	Cough
재채기	Sneeze
콧물	Runny nose
몸살	Body ache
어지러움	Dizziness
목 아픔	Sore throat

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6. Quick Quiz (Test Yourself!)

1️⃣ Fill in the blanks:

🔹 감기 _____ 집에 있었어요. (because of)
🔹 머리가 아프_____ 약을 먹었어요. (because)
🔹 피곤하_____ 일찍 자요. (since)

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2️⃣ Choose the right grammar:

🔹 (아/어서, (으)니까, 때문에)

1. 열이 나_____ 병원에 가세요.
2. 두통 _____ 일하기 힘들어요.
3. 기침하_____ 물을 마셨어요.

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3️⃣ Translate into Korean:

🔹 "I stayed home because of a fever."
🔹 "Since you’re tired, rest."
🔹 "I took medicine because I had a headache."

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Comment your answers below! ⬇️😊