기 때문에 (because of, due to)

This pattern turns an action into a noun. It uses the 기 nominalizer. Then it adds 때문에, which means "because of." Together, they mean "due to the fact that..." It works with verbs and adjectives. It even works with nouns. It creates a very strong link between two sentences. The first part is the reason. The second part is the result. It is much stronger than -아/어서. It focuses purely on the cause-and-effect relationship. Imagine you are explaining why you were late. -아/어서 sounds like a soft explanation. 기 때문에 sounds like a formal report. It is objective and direct. You are stating a truth. You are not just making conversation.

1. 1Using this grammar is quite simple. You just need the stem of the word.
2. 2For verbs and adjectives, take the stem. Add 기 때문에 directly to it. For 가다 (to go), it becomes 가기 때문에. For 바쁘다 (to be busy), it is 바쁘기 때문에.
3. 3For the past tense, attach 기 때문에 to the past tense stem. 갔기 때문에 means "because I went." 바빴기 때문에 means "because I was busy."
4. 4For nouns, you need a different bridge. Use 이기 때문에. If the noun ends in a vowel, you can drop the 이. 학생이기 때문에 (because I am a student) or 친구기 때문에 (because we are friends).
5. 5For the future tense, use -(으)ㄹ 것이기 때문에. This is often shortened to -(으)ㄹ 거기 때문에 in speech.

Use this when you want to be objective. It is perfect for writing essays. It is great for giving presentations at work. Use it when the reason is undeniable.

• In a job interview: 저는 성격이 성실하기 때문에 일을 잘 할 수 있습니다. (Because I am diligent, I can do the job well.)
• Explaining a delay: 비가 많이 왔기 때문에 기차가 늦었습니다. (Because it rained a lot, the train was late.)
• Giving a medical reason: 감기에 걸렸기 때문에 병원에 가야 해요. (Because I caught a cold, I must go to the hospital.)
• Discussing prices: 물가가 올랐기 때문에 비싸요. (Because prices rose, it is expensive.)

You are stating facts here. There is no room for doubt. It is like a grammar traffic light. Green means the reason is clear and solid.

There is one huge rule you must remember. Never use 기 때문에 with commands or suggestions. This means no -세요, -읍시다, or -ㄹ까요. It sounds very awkward. If you want to say "Because it is raining, let's stay home," do not use this. Use -(으)니까 instead. 기 때문에 is for stating what is. It is not for asking or telling people what to do. Also, avoid it for simple social greetings. You would not say "Because I met you, I am happy" using this. It is too heavy for that. It would feel like a business contract. Keep it for real reasons and facts. If you use it while apologizing, it might sound like an excuse. Stick to -아/어서 for "Sorry I am late."

One common trip-up is the noun form. Many people forget the 이 in 이기 때문에. 의사기 때문에 is okay in speech. But 의사이기 때문에 is better for writing. Another mistake is mixing up the tenses. Remember to put the tense marker *before* 기. Do not say 가기 때문에었어. Say 갔기 때문에. It is also easy to use it too much. If you use it in every sentence, you sound like a textbook. Even native speakers mess this up sometimes! They might use it with a suggestion by accident. But you are smarter than that. Just keep the "No Commands" rule in your pocket.

Let's look at the "Because" family.

• -아/어서: This is the most common. It is soft and natural. Use it for feelings and sequential actions. It is the "everyday because."
• -(으)니까: This is subjective. It is based on your opinion. "I think we should leave because..." It is the only one you can use with commands.
• 기 때문에: This is the anchor. It is objective and strong. Use it for facts and formal logic.

Think of it like this:

• -아/어서 is a handshake.
• -(으)니까 is a finger point.
• 기 때문에 is a signed document.