There are many grammar phrases made of Verb-아/어야.
The most common ones would be :
1) Verb-아/어야 되다
2) Verb-아/어야 하다
4) Verb-아/어야 (S) + (V) ~
We already learned first two phrases : “Verb-아/어야 되다” and “Verb-아/어야 하다.
They both mean “to have to verb,” and can be used interchangeably. (Check Beginner2-Lesson 19)
내일 시험이 있어서 공부를 열심히 해야 돼요. I have an exam tomorrow, so I have to study hard.
=내일 시험이 있어서 공부를 열심히 해야 해요.
이따가 엄마가 오셔서 집을 치워야 해요. Mom will be coming later today, so I have to clean the house.
=이따가 엄마가 오셔서 집을 치워야 돼요.
“야” in Verb-아/어야 indicates “you should/need/have to” do something.
With this in mind, let’s look at Verb-아/어야겠다.
Now that know what Verb-아/어야 is, what is -겠다 that’s attached right after?
We learned that 겠다 is one of the future tenses in Korean (check Beginner2-Lesson8)
So Verb-아/어야겠다 literally translates to “will have to verb.”
This can further translate to “had better” or “I guess one should~” in English.
As you can see from its English translation, it’s a less stronger version of should/have to.
In other words, Verb-아/어야겠다 is used when something’s not necessarily required of one to do, but you think it would be best for someone (or oneself) to do that.
Now let’s compare the two sentences below.
통금이 있어서 밤 9시 전까지 기숙사로 돌아가야 해요. There’s a curfew, so I have to be back in the dorm by 9pm.
너무 졸려서 밤 9시 전까지 기숙사로 돌아가야겠어요. I’m too sleepy, so I had better return to the dorm by 9pm.
In the first sentence, Verb-아/어야 하다 indicates that it is required of you to return to the dorm because of the curfew. Almost like “must.”
In the second sentence, you feel sleepy and although it’s not a must, you “think” it would be best for you to return to the dorm before it gets too late.
Let’s look at another comparison.
사람은 잠을 자야 해요. vs 사람은 잠을 자야겠어요.
If you are trying to say “Men must sleep,” which one do you think is a correct one?
Without a doubt, it’s the first one.
Sleep is naturally required of humans to live on. Therefore, it would sound weird to say “사람은 잠을 자야겠어요 (I think men should sleep)” when it’s already a general/natural rule for humans to sleep.
Let’s try one more.
This time, if you are trying to say, “Jisoo looks tired. She should get some sleep.” Which one do you think sounds natural?
- 지수가 피곤해보여요. 잠을 자야 해요.
- 지수가 피곤해보여요. 잠을 자야겠어요.
Actually, both of the above would work, depending on how certain or assertive you want to sound on what Jisoo should do.
잠을 자야 해요 : Jisoo has to sleep.
잠을 자야겠어요 : Jisoo had better sleep, I guess she should get some sleep, She will have to get some sleep.
If you’re seriously worried for her, or you’re certain that getting sleep will make her better, you may use the first one.
If you’re worried for her but not up to a point where you want to assert what’s needed for her, you may use the second one.
Using Verb-아/어야 해요 doesn’t necessarily sound nosy or arrogant. It depends on what you consider the situation to be.
Can you feel the difference now?
Verb-아/어야겠어요 is therefore used when you want to sound less assertive about what you think someone or yourself should do. Just like “had better” or “will have to” in English.
Verb-아/어야 하다 : should (required), it’s a must-do, a general rule or even a command
Which one sounds natural?
1. While watching sick people, I thought I should become a doctor.
아픈 사람들을 보면서 의사가 되어야겠다고 생각했어요. (O) – This one sounds natural.
아픈 사람들을 보면서 의사가 되어야 한다고 생각했어요. ( )
— It’s not like it’s required of you to become a doctor, but you think that’s best for you to take care of sick people.
2. I have to submit the homework before deadline.
숙제를 마감 기한까지 제출해야겠어요. ( )
숙제를 마감 기한까지 제출해야 해요. (O) – This one sounds natural.
— Deadline is there for you to meet. Otherwise, you won’t be able to submit it at all. Therefore, it’s required of you to do.
3. I need to finish homework by this weekend. I’d better start now. (Put “야 해요” and “야 겠어요” in the right blank.)
숙제를 이번 주말까지 끝내( ). 지금 시작해( ).
숙제를 이번 주말까지 끝내(야 해요). 지금 시작해(야겠어요.)
— Finishing homework is required of you to do. However, starting now is an option that you think is best for you.