Connective Ending 아/어/여서 (because, so)

At its core, 아/어/여서 links two ideas. The first part of the sentence is the reason. The second part is what happened because of that reason. For example, if you say 배가 고파서 김밥을 먹었어요, you're saying "Because I was hungry, I ate kimbap." The hunger (배가 고프다) is the cause. The eating (먹다) is the result. It’s important to remember that the relationship between the two parts is very close. It’s not just two random facts. They are logically tied together. You can use this with both verbs and adjectives. It’s incredibly versatile. You’ll hear it in the subway, in the office, and definitely in every romantic scene where someone explains why they fell in love. It’s the ultimate "cause and effect" tool in your linguistic toolkit.

1. 1Adding this to a word is pretty straightforward. It follows the same rules as the polite ending 아/어/여요. Follow these steps to get it right:
2. 2Find the verb or adjective stem by dropping the 다.
3. 3Look at the last vowel of the stem.
4. 4If the last vowel is ㅏ or ㅗ, add -아서. For example, 가다 (to go) becomes 가서 and 오다 (to come) becomes 와서.
5. 5If the last vowel is anything else (ㅓ, ㅜ, ㅣ, etc.), add -어서. For example, 먹다 (to eat) becomes 먹어서 and 읽다 (to read) becomes 읽어서.
6. 6If the verb ends in 하다, it always changes to -해서. For example, 공부하다 (to study) becomes 공부해서 and 사랑하다 (to love) becomes 사랑해서.
7. 7Pro-tip: If the stem ends in a vowel, it usually contracts. 가 + 아서 doesn't stay as 가아서, it just becomes 가서. It’s like a grammar traffic light—keep things moving quickly!

You can use 아/어/여서 in two main ways. The most common is giving a reason. "I'm busy, so I can't go" or "It's raining, so I stayed home." It’s perfect for everyday situations. Imagine you’re at a cafe. You might say 커피가 너무 뜨거워서 못 마셔요 (The coffee is too hot, so I can't drink it). Another use is for a sequence of events. But be careful! These events must be closely related. If you go to the park and then meet a friend there, you say 공원에 가서 친구를 만났어요. The two actions are linked in time and space. You didn't just go to the park and then suddenly find yourself at home meeting a friend. The first action leads directly into the second. This makes your storytelling feel much more cohesive.

This is where many people trip up. There are two major "no-go" zones for 아/어/여서. First, never use a tense marker like 았/었 or 겠 before it. The tense of the whole sentence is decided at the very end. So, even if the reason happened in the past, you use the base form. Wrong: 먹었어서. Right: 먹어서. Second, you cannot use this grammar when you are giving a command or making a suggestion. If you want to say "Because it's raining, let's take a taxi," you can't use 아/어/여서. It just doesn't work for ~세요 (please do) or ~까요? (shall we?) endings. In those cases, you'll need its cousin, ~(으)니까. Think of 아/어/여서 as a reporter stating facts, not a boss giving orders.

Yes, even native speakers mess this up sometimes—usually when they are in a rush! The biggest mistake for you will be trying to put 았/었 in the middle of the sentence. Your brain will scream, "But it happened yesterday!" Ignore it. Keep the middle simple. Another common error is using it with greeting words in a weird way. While we say 만나서 반가워요 (Nice to meet you—literally: because we met, I'm happy), you shouldn't over-apply this logic to every greeting. Also, watch out for irregulars. 돕다 (to help) becomes 도와서, not 돕아서. If you use the wrong vowel connection, it’s like wearing socks with sandals—people will understand you, but it feels a bit "off."

You might be thinking, "Wait, isn't ~(으)니까 also 'because'?" You're right! But they have different vibes. 아/어/여서 is generally for general reasons or common-sense facts. It’s softer and more subjective. It’s great for apologies. 늦어서 죄송합니다 (I'm sorry for being late) sounds sincere. If you used 니까 there, it might sound like you're making a defensive excuse. 니까 is stronger, more objective, and as we mentioned, the only one allowed with commands. Use 아/어/여서 when you want to be polite and show a natural flow. Use 니까 when you're pointing out a clear reason for an action you're about to take or a command you're giving.