Questions:
1. Why is "him" outside []?
Because its form (that it is an object pronoun) tells us that it sits in an object position. If it sat in a subject position, its form would be 'he':
a) I want [he to come] :cross: SV
b) I want [him to come] :cross: OV
Example a) has infinitive 'to come' assigning nominative case to 'he'. The resulting *'he to come' is ungrammatical because infinitive 'to come' cannot assign case...ever. Example b) has 'him' occurring before its verb; we expect to see it following a verb (or a preposition).
c) I want him [to come] :tick:
d) I want for him [to come] :tick:
Example c) has 'him' receiving case from case-assigning 'want'; Example d) has 'him' receiving case from the preposition 'for'.
2. Why do we have a PRO once we have a "him"?
It's based on the idea that every clause has a subject and a verb.
- Verbs that assign case take an overt subject (in pro-drop languages (say, Irish, subjects can be omitted, which is where small pro comes in).
- Verbs that do not assign case (such as infinitive verbs) take PRO as their structural subject.
- 'to come' is an infinitive verb and as such cannot assign case, but semantically we know it has a doer, an agent, a subject:
- [PRO to come]
- by default PRO is semantically empty. It gains its meaning from the closest pronoun
3. Each clause has a semantic subject and a structural subject, right?
Right. In our example, 'I' is both the structural and semantic subject of the verb 'want':
'I' = structural subject: SV & case marking
'I' = semantic subject: e.g., doer, agent of 'want'
'him' = structural object: case marking
'him' = semantic subject: doer, agent of '(to) come'
PRO = structural subject: SV
PRO = semantically empty by default; gains its meaning via co-referencing with 'him', an object pronoun in the higher clause.
4. Why not "him" is both?
Well, in a way, it is both: 'him' holds an object position, structurally, in the higher clause and is tied to PRO, semantically, in the lower clause.
By the way, a given constituent can hold one and only one position in the structure.
5. Why is [] around "h" in "think?
The brackets represent an edited word. You wrote 'tink', which I corrected to 't[h]ink'.
6. Do you not think it is an absurd idea: "him" as an indirect object?
Absurd...? No more absurd than the assumption that 'him' gets case from 'to come'.
To be clear, 'want' is not a (known) IO+DO verb. It is similar in structure to causative and perception verbs, but the alternative (the accepted idea that 'to come' is an object complement) seems awkward semantically:
- I want him [to come] object complement :?:
- Object Complement Test
- He is to come
- Does 'to come' rename the subject? Cf. They call him Sam / He is Sam, wherein the object complement 'Sam' renames the subject/complements the object: semantically, he is Sam.
7. Am I right with this?
If the [] part is the C, it would follow we have an ellipted finite verb in the object complement clause. An ellipted finite verb implies a pro. English is not a pro-drop language, which means the [] part is not a C and, consequently, the sentence is not a SVOC.
The verb is elliptical, yes, but the representation was confusing. Sorry for that. I inserted '(is)' to test for an object complement.
More clearly, 'to come' doesn't seem to complement the object in the way that we would expect it to semantically:
- I want him [to come]
- He is to come <object complement test>
- Doesn't he is to come mean something different from I want him to come? (Cf., again, they called him Sam - he is Sam.)