Relative clause = Adjective clause VS participle clause = adverbial clause

[English confuse me]

There is a discrepancy below.

Relative clause = adjective clause
1. The boy who is sitting in front of you is my cousin.
Obviously, the relative clause above is adjective clause describing the boy.

However, when I rephrase the clause into an adjective phrase.
2. The boy sitting in front of you is my cousin.
Apparently, the adjective phrase becomes a present participle clause.

As we all know, participle clause = adverbial clause, for example:
3. Seeing an accident ahead, I stopped my car.
Also plainly, the participle clause above (non-finite) is adverbial clause.

So, by conjecture, Participle clauses can also be used as adjective phrases.
Have someone discover it before?

[Raymott]

There is a discrepancy below.

Relative clause = adjective clause
1. The boy who is sitting in front of you is my cousin.
Obviously, the relative clause above is adjective clause describing the boy.

However, when I rephrase the clause into an adjective phrase.
2. The boy sitting in front of you is my cousin.
Apparently, the adjective phrase becomes a present participle clause.

As we all know, participle clause = adverbial clause, for example:
3. Seeing an accident ahead, I stopped my car.
Also plainly, the participle clause above (non-finite) is adverbial clause.

So, by conjecture, Participle clauses can also be used as adjective phrases.
Have someone discover it before?

There are a few holes in your argument.
You call "sitting in front of you" a phrase, and "seeing an accident ahead" a clause. This anomaly explains how you get a phrase from a clause.

"2. The boy sitting in front of you is my cousin." Here "sitting in front of you" is participial construction acting adjectivally. That's how you make a participial X equate with an adjectival X.
It's well-known that a participle can act as an adjective.

I can't find anything noteworthy about your argument.

[panicmonger]

There are a few holes in your argument.
You call "sitting in front of you" a phrase, and "seeing an accident ahead" a clause. This anomaly explains how you get a phrase from a clause.

Actually, can a participial clause(non-finite) acting as adjective be called a phrase? In this case, it is "sitting in front of you".

According to my book, it states that there are many different types of adjective phrase such as prepositional phrase, participle phrase(non-finite clause).

In the case of participle construction, participial clause is equal to participial phrase.

From you reply, I begin to doubt the correctness of my book.

[Raymott]

Actually, can a participial clause(non-finite) acting as adjective be called a phrase? In this case, it is "sitting in front of you".

According to my book, it states that there are many different types of adjective phrase such as prepositional phrase, participle phrase(non-finite clause).

In the case of participle construction, participial clause is equal to participial phrase.

From you reply, I begin to doubt the correctness of my book.

I don't know. When I went to school, a clause had to have a finite verb. "Clause" is used differently by different grammarians.