§ 521. Most authors who do not regard parenthetical elements as parts of the sentence treat It is past ten, I think as a simple sentence 1. We do not find this view convincing. -
1. If / think is not some part of the sentence, it must
be regarded as an independent sentence. But it is not indepen
dent. Its intonation, position and meaning show that it is
connected with It is past ten, to which it is appended and on
which it depends.
2. The sentence discussed is not simple because it contains
two predications. This becomes especially evident when we
compare ft is past ten, I think with / think it is past ten.
3. Since we regard parenthetical elements as parts of the
sentence (see § 473) we must treat It is past ten, I think as a
complex sentence, i. e. a sentence having one of its parts
(parenthetical element) expressed by a clause (a parenthetical
clause).
§ 522. In most cases parenthetical clauses are introduced asyndetically, though now and again the conjunctions as, if, etc, are used.
He is, as I told you, their only son. (Dickens). - The happiness was a private, tf you like, a happy one. (Snow).
Like parenthetical words and word-combinations they express the speaker's attitude towards the contents of the sentence or they show the relation of the given thought to some thought previously mentioned or to the source of information.
Nursing a wounded heart, he thought cynically, would not lead to happiness. (Randall).