Here are my thoughts regarding your questions. I have rendered your statements and questions in blue text, my answers in black text:
I thought of two statements that I tried to break down applying what I had learned. Could you help me with some of the gaps?
(a) "She likes spaghetti more than I do."
(1) "She likes spaghetti" is an independent clause. That’s right.
(2) "I do" is an elliptical clause. That’s right. “I do” is an elliptical construction of the full clause “I like spaghetti.” Without the ellipsis, of course, that sentence will read as follows: "She likes spaghetti more than I like spaghetti.” The ellipsis streamlines the sentence by eliminating the repetition of the phrase “like spaghetti,” which doesn’t sound very nice both in written and spoken form.
(3) "more than" joins the two clauses together. Since coordinating conjunctions are limited to the fanboys mnemonic, does it follow that this is a conjunctive adverb?No, “more than” isn’t a conjunctive adverb; it’s actually a combination of the adjective “more” and the preposition “than,” forming the comparative “more than.” Recall that when a conjunctive adverb links two clauses that comprise a sentence, the conjunctive adverb needs to be preceded by a semicolon. The comparative “more than” doesn’t have that form and, as such, doesn’t qualify as a conjunctive adverb.
(4) Do elliptical clauses inherit all the rules an independent clause would have? (e.g. it must contain a subject and predicate, a coordinating conjunction to link it with another independent clause)Generally, but not always. Two independent (coordinate) clauses, one of which is elliptical, can sometimes be joined by a semicolon alone, as in: “She doesn’t believe in beginner’s luck; I do.” (Of course, the usual form for that sentence uses the coordinate conjunction “but”: “She doesn’t believe in beginner’s luck,
but I do.”
(b) "She is quite happy where she is, as am I." The elliptical clause “am I” isn’t in the proper form above; it’s in the interrogative form. Instead, that sentence should read as follows: "She is quite happy where she is,
as I am*."
(1) "She is quite happy where she is" is an independent clause. That’s right.
(2) "as" is a subordinate conjunction. That’s right.
(3) "am I" is, well, I'm not sure but is this also an elliptical clause (I am quite happy as well) since it is preceded by the subordinate conjunction "as", a conjunction that makes an independent clause dependent?Not “am I,” but “I am.” As such, it’s an elliptical clause for “I am quite happy where I am” in this full sentence: "She is quite happy where she is
as I am quite happy where I am.” (Depending on the meaning intended by the speaker, the full sentence could also be as follows: "She is quite happy where she is
as I am quite happy where she is.”)
(4) Should there be a comma in the statement?No; coordinate clauses joined by “as” don’t require a comma between them. This is a very common mistake when “as” is used as a coordinating conjunction.
(5) Can a comma also be a grammatical device that joins two clauses together?Yes, in the very rare usage of the so-called
tricolon, as in triumphant Julius Caesar’s boast: “I came, I saw, I conquered.” The tricolon, as we can see, consists of three parallel phrases of perfectly identical length; it is primarily used as a rhetorical device. (From a strict grammar standpoint, that sentence should be using semicolons instead: “I came; I saw; I conquered.” Or, for the usual over-the-counter English, it should eliminate the two other “I’s” and add a comma before the last verb: “I came, saw,
and conquered.”
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*Let me just add this further clarification: The "am I" ending for sentences with parallel coordinate clauses apply only when the coordinating conjunction "so" is used, not when "as" is used. Examples: "You are happy and
so am I." "I was happy about the turn of events and
so were my close friends." We don't say: "You are happy and
so I am." "I was happy about the turn of events and
so my close friends were." In such "so"-using sentences, it's idiomatic for the "am," "was," or "were" form of the verb "be" to always precede the noun or pronoun in the second coordinate clause.
The
BBC World Service Learning English web page has has an excellent explanation and drill for the form "so do I" and "me too." Just click the link to check it out.