What is the difference in usage between the endings 다고 and 대?

Question

Is there a difference in usage between the endings 대(요) and 다고(요) ? I seem to hear 다고 (and the closely related 라고) used more in spoken language, but I think there is a little more to the story...I know they are both abbreviated quotations (I/you/he/she/they/someone says ~) but I think there is a bit more to the story here...

Answer 1

Catomic's answer showed many good examples of using -다고 inside a sentence, so I'll just talk about using it at the end of the sentence.

If you end a sentence with -다고 (or -라고/-자고/-냐고), I think it almost always quotes the speaker's own speech. E.g., imagine a noisy place:

A: 저녁 먹으러 갈까?

B: 벌써 먹었는데.

A: 응, 뭐라고?

B: 벌써 먹었다고. (= (I said) I already ate dinner.)

Be careful, because in other situations, it may sound argumentative, just like English "I said".

A: 주말에 뭐 할까?

B: 주말에 시간 없다고. (~= I said I don't have time at the weekend. Didn't you listen?)

On the other hand, -대 is always used to quote someone else. (I can't think of any case I could use -대 to quote myself.) For example:

A: 저녁 먹으러 갈까?

B: 좋지. 가자.

A: 민수는 안 간대? (= What about Minsoo? (literally, "Does Minsoo say he isn't going?"))

B: 벌써 저녁 먹었대. (= He says/said he already ate dinner.)

Answer 2

-대 is simply an abbreviation of -다고 해 in Korean. For example:

철수가 밥을 먹었다고 해요.

철수가 밥을 먹었대요.

Check out the answer of the National Institute of the Korean Language(국립국어원):

'-대' is an abbreviation of '-다고 해', which is used to tell people what others said, and not what you experienced.

Answer 3

하다 has a sense of 'to say.' If Youngjoo says:

만수가 똑똑하다 (Mansoo is smart)

reporting it would have the base form of:

영주가 만수가 똑똑하다고 하다 (Youngjoo says Mansoo is smart)

which may become, depending on the level of respect for the addressee:

• 영주가 만수가 똑똑하다고 해.
• 영주가 만수가 똑똑하다고 해요.
• 영주가 만수가 똑똑하다고 합니다.

which respectively contract to

• 영주가 만수가 똑똑하대.
• 영주가 만수가 똑똑하대요.
• 영주가 만수가 똑똑하답니다.

Ending a sentence with 다고, as in B's reply below:

A: 영주가 뭐라고 그러니?
B: 만수가 똑똑하다고 (해).

is simply leaving out the last 하다 (for to say). It is comparable to:

A: What does Youngjoo say?
B: (Says) That Mansoo is fat.

다고요 is a quick, infomral way to raise the level of respect (given to the addressee) from 다고. You can put 요 after just about anything for a quick fix although I am not sure about its being grammatical. For example:

Pupil: 뭘 드셨나요? (What did you eat sir?)
Master: 국수. (Noodles child.)

But,

Master: 뭘 먹었니? (What did you eat child?)
Pupil: 국수요. (Noodles sir.)

One thing to note is that '이다' becomes '이라' as part of what is being reported, e.g.:

• 만수가 장남이다. (Mansoo is the eldest son.)
  → 영주가 만수가 장남이라고 해. (Youngjoo says that Mansoo is the elderst son.)
  → 영주가 만수가 장남이래.
  
• 만수가 갈 것이다. (Mansoo will go.)
  → 영주가 만수가 갈 것이라고 해 (or 갈 거라고 해). (Youngjoo says Mansoo will go.)
  → 영주가 만수가 갈 것이래 (or 갈 거래).

Other tenses and moods can be reported too.

• 만수가 갔다. (Mansoo went.)
  → 영주가 만수가 갔다고 해. (Youngjoo says Mansoon went.)
  → 영주가 만수가 갔대.
  
• 만수를 보내자. (Let us send Mansoo.)
  → 영주가 만수를 보내자고 해. (Youngjoo says to send Mansoo.)
  → 영주가 만수를 보내재.

If Youngjoo's utterance took place in the past:

• 만수가 갔다. (Mansoo went.)
  → 영주가 만수가 갔다고 했어. (Youngjoo said Mansoon had gone.)
  → 영주가 만수가 갔댔어.
  

Finally, most of the times, 그러다 can replace 하다 for to say without sounding any less idiomatic. Thus,

• 영주가 만수가 똑똑하다고 그래. (Youngjoo says Mansoo is smart.)
• 영주가 만수가 똑똑하다고 그랬어. (Youngjoo said Mansoo was smart.)

sounds just as natural, but -다고 (or -라고) + 그러다 cannot be contracted.

말하다 in place of 하다 or 그러다 is no longer the same thing. It sounds rather formal, like to state.