는 것 Principle
Hiii :)

I am right now having trouble with ending sentences using the 는 것 principle. I get confused if I can end the sentences with just 거/게, 것을, 것은, etc.

For example:
학교에 있는 거야? - Does that mean - Are you at school?

I get confused with how the 거, 것을 것은 part is connected to the 는 part.

For example:

책을 읽는 것을 좋아해요. Why should the 것을 be there? Does it "call onto" the 책을 part? It seems like there's two objects with 을 that are being connected with 좋아해요. I almost read it from middle, then right, then left. "Things that are good are reading books." Is it correct to think that way?

Can anyone clarify this principle a bit more? Thank you.

Question

는 것 Principle
Hiii :)

I am right now having trouble with ending sentences using the 는 것 principle. I get confused if I can end the sentences with just 거/게, 것을, 것은, etc.

For example:
학교에 있는 거야? - Does that mean - Are you at school?

I get confused with how the 거, 것을 것은 part is connected to the 는 part.

For example:

책을 읽는 것을 좋아해요. Why should the 것을 be there? Does it "call onto" the 책을 part? It seems like there's two objects with 을 that are being connected with 좋아해요. I almost read it from middle, then right, then left. "Things that are good are reading books." Is it correct to think that way?

Can anyone clarify this principle a bit more? Thank you. <33Would it also be ok to have the sentence as: 학교에 있는 거?

Answer

From https://www.koreanclass101.com/forum/viewtopic.php?t=2588

Let's Break --는 것 
First, Here, --"는" is sort of usage of "to verb" or "V+--ing". 
For examples, 
보다 "see" becomes 보 (verb-stem) + 는 = 보는 (seeing, to see) 
하다 "do" becomes 하 (verb-stem) + 는 = 하는 (doing, to do) 
먹다 "eat" becomes 먹 (verb-stem) + 는 = 먹는 (eating, to eat) 
배우다 "learn" becomes 배우 (verb-stem) + 는 = 배우는 (learning, to learn)

Now, let's take a look at "것". 
"것" is 'Possessive Pronoun' that attaches to 'adjective' or 'Verb + -ing' (most times) and help the phrase to become NOUN. 
Remember this - in the sentence, A is B, A must be NOUN or Noun phrase.

"Seeing is believing" = 보는 ("seeing" - adjective) + 이다 ("is" - verb) + 믿는 ("believing" - adjective) 
If I literally translate it, "Seeing is believing" becomes 보는 믿는 이다, which is NOT a Korean sentence at all. 
HOWEVER, you can make it correct by attaching 것 right after 'Verb+ing' and, it becomes NOUN!!!

보는 "seeing" + 것 "possessive pronoun" = 보는 것 (FINALLY "seeing" becomes NOUN) in Korean.

Okay, I hope now you understood some of this grammar rule. 
Okay, go back to "Seeing is believing" = (literal translation) is 보는 믿는 이다. 
Now you know how to make 'Verb+ing' into NOUN by attaching 것. 
"Seeing" 보는 + 것 "Possessive Pronoun" = 보는 것 "seeing (NOUN)" 
"Believing" 믿는 + 것 = 믿는 것 "believing (NOUN)" 
Finally, the correct translation for "seeing is believing" is 보는 것 + 은(Topic Marking Particle) 믿는 것 이다. 
보는 것은 믿는 것이다. "seeing is believing" 
"Doing is necessary" 하는 것은 필요하다. 
"Eating is essential" 먹는 것은 필수적이다. 
"Learning Korean is my dream" 한국어를 배우는 것은 + "learning Korean" 내 꿈 + "my dream" 이다 "is" 
=한국어를 배우는 것은 내 꿈이다. 
Same thing with "My dream is to learn Korean." = 내 꿈은 "my dream" + 한국어를 배우는 것 "learning Korean" + 이다 "is" 
=내 꿈은 한국어를 배우는 것이다.

Answer

"~는 것" is one of the forms that make a noun out of a verb like gerund in English.

For example, if you want to say "I like to read books", or "I like reading books", these are the steps involved.

1. I read books = 나는 책을 읽는다. (읽는다 is the present tense of 읽다, the root form)
2. reading books = 책을 읽는 것 (the act(것) of reading (읽는) books(책을)) - a noun phrase.
3. I like [reading books] = (나는) [책을 읽는 것]을 좋아해요. (나는 is often omitted as it is obvious)

So 책을 읽는 것 functions as the object of the verb 좋아해요 (like).
The key things is that any verb phrase and sentence can be converted to a noun phrase by adding ~는 것.

Example:
- what I like = that(것) which I(내가) like(좋아하다) = 내가 좋아하는 것.
- what I like the most = 내가 제일 좋아하는 것. (제일=the most) - the phrase can expand as needed.
- What I like the most is my puppy = 내가 제일 좋아하는 것은 우리 강아지이다. (우리=my, 강아지=puppy, 이다=is)

There is another important use of the ~는 것 form, which is to make an indirect statement.
학교에 있는 거야 is an example, which is constructed as follows.

1. (나는) 학교에 있어 = I am at school.
2. 학교에 있는 것 = that I am at school - a noun phrase of an abstract notion.
3. [(나는) 학교에 있는 것]이야 = It is [that I am at school]. (~이다 = (it) is; 거야 is a contraction of 것이야)

In #2 a sentence (which always ends with a verb) is turned into a ~는 것 form.
Then in #3, the verb 이야 (it is) is attached to create an indirect statement of "It is [...]".
(Without the verb, it is not a complete sentence, so 학교에 있는 거 would be wrong)

This indirect sentence form is very widely used.  It has the tone of explaining something, or an objective statement
You can think of it as being similar to "It is that ..." in English.

Examples:
AA: 너 여기서 뭐 해? = What are you doing here?
BB: 학교에 가는 거야 = I am going to school.
 
It is not that I don't like you but that I need some time alone.
= (내가) 너를 좋아하지 않는 게 아니라 혼자만의 시간이 필요한 거야.

Answer

거 is colloquial short form of "것"
게 is colloquial short form of "것이"
걸 is colloquial short form of "것을"
건 is colloquial short form of "것은"

너는 학교에 있는 거야? literally means "Is it you that is at school?"
그것은 학교에 있는 거야? literally means "Is it something that is at school?"

책을 읽는 것 is a noun phrase which means "reading book"
책을 읽는 것을 좋아해요. I like reading book.

Here is the order of composition of sentence.

좋아해요. I like something.
무엇을 좋아해요? What do like?

읽는 것을 좋아해요. I like reading something.
무엇을 읽는 것을 좋아해요? What do you like reading.

책을 읽는 것을 좋아해요. I like reading book.

거 is a noun. 야 is an ending suffix.
A sentence ends with a noun is grammatically not correct.
A sentence normally ends with an ending suffix.

학교에 있는 거야? (O)
학교에 있는 거군? (O)
학교에 있는 거지? (O)
학교에 있는 거예요? (O)
학교에 있는 거네? (O)
학교에 있는 거예요? (O)
너는 학교에 있는 거? (X)

But, in colloquial language, it can be used on the context.
ex)
가방을 가져와. (Bring me a bag.) 
어떤 가방? 학교에 있는 거? (O) (Which bag? Do you mean the bag which is at school?)