-아서/-어서 (Reason & Order)

The -아서/어서 ending is a fundamental Korean concept that English speakers often struggle with because English separates cause from effect using different sentences or conjunctions (because, so, therefore), while Korean threads them together into a single, flowing causal chain.

In Korean, -아서/어서 doesn't just mean "because"—it expresses an inevitable, natural consequence that flows directly from the preceding action or state. Think of it as: "By doing X, naturally Y happens." This is why you often see it used for sequence (one thing happens, then the next thing happens *as a result*) as well as reason. For example, 비가 와서 못 갔어요 literally flows as "rain came, (and so naturally) couldn't go"—the rain itself *causes* the inability to go, not just explains it.

The key difference from English is directness and inevitability. English requires you to construct separate clauses and connect them with conjunctions, keeping cause and effect mentally separate. Korean collapses this separation—the cause *leads into* the effect seamlessly. This is why -아서/어서 works for both reasons ("I was tired, so I slept") and sequence ("I woke up, (and then naturally) got dressed"). Both are the same structure: one state/action naturally triggering the next.

Choose -아서 if the verb or adjective stem ends in a consonant or the vowel ㅏ/ㅗ; choose -어서 for all other vowels. The form is tense-neutral—you mark tense in the final verb of the sentence, not in the -아서/어서 clause itself.