How to parse 「月日の経つのは早いものだ」


> 月日の経つのは早いものだ。

From left to right, the first の marks a genitive case and the second one acts
as a nominalizer. This means that the nominalized clause 経つの is being modified
by 月日, forming a noun phrase 月日の経つの.

> 月日 **の** 経つのは早いものだ。
>

>> _lit._ The passing of time is quick!

However, we could replace the first の with が, which changes the meaning a bit:

> 月日 **が** 経つのは早いものだ。
>

>> _lit._ Time passing is quick!

Because of this, we may think that we have a relative clause although that
would require a noun to modify. To be more precise, that would require the
second の to be an indefinite pronoun, meaning something like "the one", which
wouldn't make sense. 月日が経つの is simply a nominalized clause.

* * *

In short,

  * [[月日]{Noun}] **の** [[経つの]{Nominalized clause}] = [月日の経つの]{Noun Phrase}. The の in bold acts as a **genitive case particle**.
  * [[月日が経つ]{Clause}] **の** = [月日が経つの]{Nominalized clause}. The の in bold acts as a **nominalizer**.

Where's the relative clause?

* * *

By the way, I think 速い is also possible because we're describing its
"quickness".




  1. 月日 **の** 経つのは早いものだ。
  2. 月日 **が** 経つのは早いものだ。

These sentences are syntactically exactly the same. Changing の to が doesn't
change the meaning of the sentence a bit. The particles after 月日 are
**subject** markers, and 月日{が/の}経つ is fundamentally a relative clause that
modifies の (which is a noun).

Have you wondered why there is something called "ga-no conversion" in modern
Japanese? You may believe が is the subject marker and の is the genitive case
particle, but this distinction is rather new. In the past, these were almost
the same particle. Both could mark a subject, and both could work as a
possessive particle.

  * [Why can の and が both mark subjects in relative clauses?](https://japanese.stackexchange.com/q/28200/5010)

> Old Japanese, as far as we can tell, didn't have a dedicated subject marker
> - if you wanted a subject that wasn't the topic also, you just left it
> unmarked. It had two genitive particles, though, *nə and *ŋga (modern の and
> が); which varied according to a kind of animacy hierarchy - *ŋga with
> personal pronouns and names IIRC (I've forgotten some of the details), *nə
> with the rest.

  * [「が」vs「の」 with possessives](https://japanese.stackexchange.com/q/39264/5010)
  * [Why is there a が in 深淵に臨むが如し?](https://japanese.stackexchange.com/q/70684/5010)
  * [【古典】古文の格助詞「が」「の」(主格・連体修飾格・同格)](https://kb-study.com/kaku-gano/)

Although が and の have become very different in modern Japanese, this is why
they are still interchangeable inside "relative clauses".

And the concept of "relative clauses" is a bit broader than the English
equivalent. What you know as nominalizers and cleft sentences are actually a
special type of relative clause! Ga-no conversion works also inside these
constructions, as shown below (S = subject marker, A = attributive form of a
verb/adjective/copula, N = modified noun):

  * 太陽 **が** S昇るAのNを見ていた。  
太陽 **の** S昇るAのNを見ていた。  
I was watching the sun rising.

  * 彼 **が** S来るAのNは知らなかった。  
彼 **の** S来るAのNは知らなかった。  
彼 **が** S来るAことNは知らなかった。  
彼 **の** S来るAことNは知らなかった。  
I didn't know that he would come.

  * 彼 **が** S知っているAことNを教えてください。  
彼 **の** S知っているAことNを教えてください。  
Please tell me what he knows.

  * 彼女 **が** S1読んだA1のN1は表紙 **が** S2赤いA2本N2です。  
彼女 **の** S1読んだA1のN1は表紙 **の** S2赤いA2本N2です。  
It is a red-covered book that she read. (cleft sentence)

  * 月日 **が** S1経つA1のN1 **が** S2早いA2ことN2 **が** S3嫌いなA3理由N3 **が** S4分からないA4人N4 **が** S5したA5質問N5  
月日 **の** S1経つA1のN1 **の** S2早いA2ことN2 **の** S3嫌いなA3理由N3 **の** S4分からないA4人N4 **の**
S5したA5質問N5  
a question made by someone who doesn't understand the reason why some people
dislike the fact that time passes quickly

Notice the S-A-N pattern seen consistently in these examples. Don't mix the の
as a subject marker (marked with S) and の as a formal noun (marked with N).

So, after looking at these examples, haven't you started to think it's not
very meaningful to treat one as a subject marker and the other as a genitive
case particle? I'm not suggesting you should stop using the term nominalizer,
but it's worth knowing all of these are ruled by the same principle.




  1. 月日 **の** 経つのは早いものだ。
  2. 月日 **が** 経つのは早いものだ。

These sentences are syntactically exactly the same. Changing の to が doesn't
change the meaning of the sentence a bit. The particles after 月日 are
**subject** markers, and 月日{が/の}経つ is fundamentally a relative clause that
modifies の (which is a noun).

Have you wondered why there is something called "ga-no conversion" in modern
Japanese? You may believe が is the subject marker and の is the genitive case
particle, but this distinction is rather new. In the past, these were almost
the same particle. Both could mark a subject, and both could work as a
possessive particle.

  * [Why can の and が both mark subjects in relative clauses?](https://japanese.stackexchange.com/q/28200/5010)

> Old Japanese, as far as we can tell, didn't have a dedicated subject marker
> - if you wanted a subject that wasn't the topic also, you just left it
> unmarked. It had two genitive particles, though, *nə and *ŋga (modern の and
> が); which varied according to a kind of animacy hierarchy - *ŋga with
> personal pronouns and names IIRC (I've forgotten some of the details), *nə
> with the rest.

  * [「が」vs「の」 with possessives](https://japanese.stackexchange.com/q/39264/5010)
  * [Why is there a が in 深淵に臨むが如し?](https://japanese.stackexchange.com/q/70684/5010)
  * [【古典】古文の格助詞「が」「の」(主格・連体修飾格・同格)](https://kb-study.com/kaku-gano/)

Although が and の have become very different in modern Japanese, this is why
they are still interchangeable inside "relative clauses".

And the concept of "relative clauses" is a bit broader than the English
equivalent. What you know as nominalizers and cleft sentences are actually a
special type of relative clause! Ga-no conversion works also inside these
constructions, as shown below (S = subject marker, A = attributive form of a
verb/adjective/copula, N = modified noun):

  * 太陽 **が** S昇るAのNを見ていた。  
太陽 **の** S昇るAのNを見ていた。  
I was watching the sun rising.

  * 彼 **が** S来るAのNは知らなかった。  
彼 **の** S来るAのNは知らなかった。  
彼 **が** S来るAことNは知らなかった。  
彼 **の** S来るAことNは知らなかった。  
I didn't know that he would come.

  * 彼 **が** S知っているAことNを教えてください。  
彼 **の** S知っているAことNを教えてください。  
Please tell me what he knows.

  * 彼女 **が** S1読んだA1のN1は表紙 **が** S2赤いA2本N2です。  
彼女 **の** S1読んだA1のN1は表紙 **の** S2赤いA2本N2です。  
It is a red-covered book that she read. (cleft sentence)

  * 月日 **が** S1経つA1のN1 **が** S2早いA2ことN2 **が** S3嫌いなA3理由N3 **が** S4分からないA4人N4 **が** S5したA5質問N5  
月日 **の** S1経つA1のN1 **の** S2早いA2ことN2 **の** S3嫌いなA3理由N3 **の** S4分からないA4人N4 **の**
S5したA5質問N5  
a question made by someone who doesn't understand the reason why some people
dislike the fact that time passes quickly

Notice the S-A-N pattern seen consistently in these examples. Don't mix the の
as a subject marker (marked with S) and の as a formal noun (marked with N).

So, after looking at these examples, haven't you started to think it's not
very meaningful to treat one as a subject marker and the other as a genitive
case particle? I'm not suggesting you should stop using the term nominalizer,
but it's worth knowing all of these are ruled by the same principle.

