***** NOT A TEACHER *****
Hello, Mfhaq:
I have great news for you: You can call it a noun clause or an adverbial clause -- depending on which expert you
choose to believe.
I am honored to present the views of three reputable grammar books. These are not my views. Those books are
"old." They contain information that good high school students were taught, especially in the 20th century. I have
absolutely no idea how university-level linguistics analyzes such a sentence.
1. From Descriptive English Grammar (second edition, 1950) by Professors Homer C. House and Susan Harman. (This is my favorite grammar book for understanding high-school level grammar, especially since it contains Reed-Kellogg diagrams. If you can get a copy, you will not regret it.)
a. "He is certain that he cannot fail.
i. The two scholars say that it is a noun clause.
. (a) Their reasoning: Maybe that sentence was originally something like: "He is certain of this fact (that he cannot fail).
As you can see, "that he cannot fail" is a noun clause in apposition with the noun "fact." (page 380)
(b) Those two scholars are my heroes, so that is the theory that I personally have adopted.
2. One book called A Grammar of Present-Day English (1963) by R.W. Pence and D.W. Emery says this (page 180):
"Inasmuch as anything modifying an adjective is by that fact adverbial in function, it seems simpler to call such
clauses adverbial clauses in the first place." (My emphasis.)
3. Another very helpful book is English Review Grammar (Fourth edition, copyright renewal 1968) by Mr. Walter Kay Smart. On pages 108 -109, he says in "He is sorry that he came," "that he came" is an adverbial clause that completes the meaning of the adjective. He agrees with tzfujimino's excellent explanation. That is, "He is sorry that he came" has a
"meaning somewhat" like that of "He was sorry because he came."
4. It is clear that a fair-minded high school teacher would never ask this question on an examination, for there are at least two "correct" answers.
Sincerely yours,
James