What does it mean when we add 이/가 on to the object of the verb?

Question

I've seen 그 것이 알고 싶다 translated as 'that's what I want to know', and 사과가 먹고 싶어요 translated as 'It’s the apple (in particular) that I want to eat'.

In both of these sentences, it looks like 이/가 is being used on the verb object, not the subject. It seems to have a kind of 'emphatic' or 'indicative' flavour, but why would we not just use 는/은 for that (그 것은 알고 싶다 , 사과는 먹고 싶어요)?

Edit: It may be that, as with the English "The apple is what I want to eat", the apple isn't in fact an object, but that v + 고 싶다 behaves like a descriptive clause in this case. If so, how would this grammatical construction be described?

Answer 1

To answer the very question asked,

why would we not just use 는/은 for that (그 것은 알고 싶다 , 사과는 먹고 싶어요)?

that's because it would sound very strange.

I can assure you that no native speaker would say

그것은 알고 싶다

in isolation. He might say:

그것은 알고 싶고, 이것은 알고 싶지 않다.

Here the contrast justifies 은 and 는.

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I find your hypothesis of 그것이 or 사과가 acting as de facto subject quite insightful.

Grammar is after all only a theory. The aim is to reduce all phenomena (here, usages) to a decent set of basic concepts. Because the number of such concepts should not be too great, we sometimes have to make awkward choices. The choice could go either way. That is to say, internally consistent grammar would be possible in which 그것이 or 사과가 is either subject or object.

The awkwardness comes out well if you consider this (different) example:

나는 배가 아프다.

If you say that 나는 is subject and 배가 a complement, then it preserves the principle that a sentence should have only one subject. This however comes at the cost of having to say that, in

배가 아프다

배가 is subject. Conversely if you want consistency of treatment for 배가, you may have to allow a sentence having two subjects sometimes. No doubt some other treatment is also possible.

You may come to a quandary like this in any language I believe. For example, 'convince me that P' sounds rather like 'give me that book'; and it would be internally consistent grammar to say that 'me' was indirect object in both cases (or, if you will, dative). But some people will get vehement about what they learned in Mrs. Gault's honors English back when.

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Further on your hypothesis, consider:

This car rides well.

There are two things we can say.

1. 'Car' is the subject. But 'ride' has a different meaning than in 'I ride alone.' It means something like 'is ridden well.'

2. 'Car' is the object in spite of heading the sentence. The sentence is simply 'Null-object rides this car well.' We use this construction when we want to say that anyone would find that he could well ride a particular car.

(Those who wish, may now get vehement about 1 being right and 2 wrong, or perhaps both being wrong.)

What Korean grammar has done for,

사과가 먹고 싶다.

is analogous to 2. That is, it has paid the price of assigning multiple syntactic roles to 이/가 so as to keep the semantics of 먹고 싶다 simple.

But there is nothing to prevent you from doing 1. I.e. to say that 사과가 is the subject, but that 먹고 싶다 has a different meaning, something like that of 'is desired for eating'--if that helps comprehension. (But obviously not on an exam.)

Answer 2

I'm not professionally trained so take it with a grain of salt.

The usage of 은/는, 이/가, and 을/를 is very subtle. It has a lot to do with emphasis, the context, and your nuance.

Suppose we have A and B having a conversation.

Example 1: They are pretty much interchangeable.

A: 무엇을 먹고 싶으세요?
B: 저는 사과가 먹고 싶어요. / 저는 사과를 먹고 싶어요.

Example 2: 이/가 adds slightly more emphasis on the object.

A: 딸기를 드실래요?
B: 아뇨, 저는 사과가 먹고 싶어요.

You could say 사과를, in which case the whole sentence would have the nuance of "I want to eat an apple in general," where as saying 사과가 feels more like "I prefer apple over the alternative" or "I'm craving apples right now."

Example 3: 을/를 is a must with 싶어하다.

A: 친구 분께 드릴 딸기예요.
B: 제 친구는 사과를 더 먹고 싶어해요.

Example 4: You can use 이/가 for both the subject and object in the same sentence.

A: 제 사과를 왜 뺏어가세요?
B: 제가 딸기보다 사과가 더 먹고 싶어서 그래요.

Just like example 2, using 을/를 would have less emphasis.

I think this usage is informal, but I'm honestly not sure. In colloquial talk, though, we tend to omit the object particle anyway so you're fine :^)

Answer 3

Always look at the dictionary, they always got most of the usage covered:

이27

조사

-i (받침 있는 체언 뒤에 붙어)

1. 어떤 상태를 보이는 대상이나 일정한 상태나 상황을 겪는 경험주 또는 일정한 동작의 주체임을 나타내는 격 조사. 문법적으로는 앞말이 서술어와 호응하는 주어임을 나타낸다.

    산이 높다   
    달이 밝다   
    눈이 온다   

    오래간만이라 반가움이 더했다.
    내 친구는 책이 많다.

2. (‘되다’, ‘아니다’ 앞에 쓰여) 바뀌게 되는 대상이나 부정(否定)하는 대상임을 나타내는 격 조사. 문법적으로는 앞말이 보어임을 나타낸다. 바뀌게 되는 대상을 나타낼 때의 ‘이’는 대체로 조사 ‘으로’로 바뀔 수 있다.

    물이 얼면 얼음이 된다.
    너는 선생이 되어라.
    드디어 동생이 학생회장이 되었다. 

    그 넓던 갈대밭이 모두 뽕밭이 되었다.
    그것은 쉬운 일이 아니다.
    그 사람은 학생이 아니다.
    이것이 아니고 저것이다.
    열이 아니라 스물이라도 좋다.

-ii

1. (받침 있는 일부 부사 뒤에 붙어) 앞말을 지정하여 강조하는 뜻을 나타내는 보조사. 흔히 뒤에는 부정적인 표현이 온다.

    힘껏 도와주겠다더니, 힘껏이 겨우 이거야?

2 . (‘-고 싶다’ 구성에서 본동사의 목적어나 받침 있는 부사어 뒤에 붙어) 앞말을 지정하여 강조하는 뜻을 나타내는 보조사. (in '-고 싶다' constructions, attached after the main verb's object or the predicate modifier with a final consonant) An auxiliary particle that emphasizes the word that it's attached to.

    나는 백두산이 제일 보고 싶다.
    나는 김밥이 먹고 싶다.

3 . (받침 있는 체언이나 부사어 뒤에 붙어) 앞말을 지정하여 강조하는 뜻을 나타내는 보조사.

    도대체 우리 행동이 무엇이 잘못되었다는 거야?

The definition we're interested in is ii-2. It specifically says that '이' is used as an auxiliary particle(not the subject case marker) with -고 싶다 constructions.

Answer 4

• 이/가 suffix has over dozen different meanings, all depending on context. But for your example, they are considered to be 주격 조사(主格 助詞 - Nominative Case Particle).¹

• 는/은 suffix is considered to be 보조사(補助詞 - Auxiliary Word).¹

In a sentence, a word that has 는/은 attached to it is often the Topic Word of the sentence. A sentence that intends to clearly point out the subject within a sentence attaches 이/가 to the end of said subject. A sentence that intends to reiterate the subject presented beforehand attaches 는/은 to the end of said subject.

For example, I'll ask you a question: 당신의 목적이 뭡니까? (What is your goal?)

And, you could reply like this: 이것이 나의 목적입니다. (This is my goal.)

Notice how -이 was used to highlight the subject of the sentence. Alternatively, you could reply in a different way:

나의 목적은 이것에 관한 것입니다. (This is what my goal is all about.)

Here, -은 was used to reiterate the subject instead.

-가 is attached to 체언(體言 - Substantives/Nouns) with ending word that has no supporting consonants.

-이 is attached to 체언 with ending word that has supporting consonants.

-는 is attached to 체언, 부사(副詞 - Adverbs), and some 연결어미(連結語尾 - 'Connecting Endings')¹ with ending word that has no supporting consonants.

-은 is attached to 체언 and 부사 with ending word that has supporting consonants.

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Edit: busukxuan pointed out that I have not said much regarding 이/가 and 는/은 usage with objects.

A sentence that intends to compare and contrast two different objects, or to create emphasis on the topic object of the sentence, uses 는/은 with objects.

You asked why one would use 이/가 instead of 는/은 when dealing with objects. Let me use the examples you gave:

• 그 것은 알고 싶다: -은 makes the word 것 distinct from the rest of the sentence, marking it as the main topic of the sentence.
• 그 것이 알고 싶다: This sentence is equally grammatically valid as the sentence above; this time, the -이 makes no special distinction, and the word 것 is not marked as the main topic of the sentence.

If one wished to make no special distinction for the main topic of the sentence, they would use 이/가 instead.

1: This is my own translation. Take it with a grain of salt.