sentential modifiers(?) and relative clause question

Question

I just finished Japanese level 2 in college, which as I have come to understand is ~the most important~ and I came away with quite a lot of questions.

We learned about relative clauses and something my teacher referred to as a "sentential modifier" and they seem very similar, but clearly have different functions. Hoping someone could help.

コーヒーを飲んでいる男の人です。

the man drinking coffee

So as I understand this is an example of a relative clause (i.e. the preceding clause modifies the noun). However, when my sensei brought up a "sentential modifier" she kind of glossed over it. But here was the sentence

これは私が使う水です。

That is the water I use.

So, these things are pretty similar, but I was hoping someone could clarify this for me. Both sentences use the short form of verbs and no particle between the verb and the ~leading~ noun.

If these are both correct, how commonly are clauses/sentences like this used? Are there any "rules" about use of particles in these instances?

Answer 1

• S1. 　コーヒーを飲んでいる男の人です。 == Here's a man (who is) drinking coffee. ( a relative clause ? )

• S2. 　これは私が使う水です。 == This is the water [that I use].

The latter is said to contain a "sentential modifier" because instead of [that I use], it could be [that Peter uses] or (based on) any elaborate sentence.

e.g. 　「これは、頭が赤い魚を食べた猫と私が飲む水です。」

I think the main difference is whether the [relative clause] contains a subject or not -- (I mean "subject" in the sense of English grammar.)

Answer 2

I may not understand your question exactly but I try to answer.

If a sentence or a phrase modifies a noun, a postpositional particle isn't necessary like コーヒーを飲んでいる男, 私が使う水.

If a noun or noun phrase modifies a noun, a postpositional particle の is necessary like 男の人, 図書館の本, 大きく成功した会社の社長.

Answer 3

I can't (at least instantly) think of any relative clause which use special particle to connect to the noun.

So I suppose answer is:

• They are both commonly used grammer
• No. There is no Japanese grammer which use special (or, dedicated...?) particle to connect a relative clause to a noun.