Ought to: -아/어야지(요)

This pattern is built on the foundation of the -아/어 connective. If you already know how to conjugate the polite present tense (-아요/어요), you are 90% of the way there. You simply take that base and attach 야지. If you want to be polite to others, you add 요 at the very end to make it 야지요. In casual speech among friends, just 야지 is perfect. It functions like a sentence ending that carries the weight of necessity. It is like putting a stamp of "this is necessary" on your verb. It works primarily with verbs because it describes actions that should be taken. You will rarely see it with adjectives unless you are describing a state that someone *ought* to maintain, but even then, it usually shifts into a verb form.

1. 1Getting the form right is a three-step dance.
2. 2Find the verb stem by dropping 다 from the dictionary form. For example, 먹다 becomes 먹.
3. 3Look at the last vowel of the stem. If it is ㅏ or ㅗ, add -아야지. For example, 가다 becomes 가야지.
4. 4If the vowel is anything else, add -어야지. For example, 먹다 becomes 먹어야지.
5. 5For 하다 verbs, they always change to 해야지. It is a quick shortcut you will use constantly.
6. 6If the verb stem ends in a vowel, the 아/어 often merges. 보아야지 becomes 봐야지. It is like a quick contraction to keep the conversation flowing. Don't worry, even native speakers trip over irregulars sometimes, but the ㅏ/ㅗ rule will get you through most situations.

There are three main scenarios where this grammar shines.

First, use it for Self-Determination. This is when you are talking to yourself. "I really should exercise today" would be 운동해야지. It is like a mental sticky note. You are setting an intention.

Second, use it for Giving Advice. When your friend is tired, you say 좀 쉬어야지 (You should rest a bit). It sounds caring but firm. It is the kind of thing a mother says to a child or a close friend says when they are worried about you.

Third, use it in Real-World Scenarios. Imagine you are at a restaurant and the food is amazing. You might tell your friend, 너도 이거 먹어봐야지! (You really ought to try this!). Or, if you are lost and asking for directions, someone might tell you, 저기서 오른쪽으로 가야지요 (You should go right over there). In a job interview, if you want to show your resolve, you might say 열심히 해야지요 (I must work hard). It shows you have the right attitude.

You should avoid this pattern in very formal, cold, or official settings. If you are writing a legal contract or a formal military report, this is too soft and personal. In those cases, use -아/어야 합니다. Also, be careful using the casual -아/어야지 with people older than you or people in higher positions. Even with 요, it can sometimes sound like you are "teaching" them what to do. If your boss is late, don't say 빨리 와야지요 unless you want a very awkward talk in the breakroom. It is best used with peers, younger people, or when talking to yourself.

A classic mistake is confusing -아/어야지 with the future tense -ㄹ게요. While both can show intention, -아/어야지 focuses on the obligation or the "should" aspect. Another pitfall is forgetting vowel harmony. Saying 먹아야지 instead of 먹어야지 sounds a bit like wearing your shoes on the wrong feet—people will understand you, but it feels slightly off. Also, remember that 야지 is for close friends. If you use it with a stranger, you might come off as a bit too pushy or overly familiar. Think of it like a grammar hug; you don't just hug everyone you meet on the street!

You might wonder how this differs from -아/어야 되다/하다.

• -아/어야 되다/하다 is the standard way to say "must." It is objective. "I must go because the bus is leaving."
• -아/어야지(요) is subjective. It is about your will or your strong suggestion. "I should go (because I want to be a better person)."

Think of -아/어야 되다 as the law and -아/어야지 as your conscience. One is an external requirement, the other is an internal drive. Also, -아/어야지 is much more common in spoken conversation than in formal writing.