As the title suggests, would you consider the following sentence grammatically incorrect (not awkward, INCORRECT)?
The chair was too small for him to sit on it.
The sentence would make a better sentence without "it" at the end, but would including "it", nevertheless, make it grammatically incorrect?
There's nothing syntactically wrong with repeating the subject (optionally, using a pronoun), but in OP's specific example doing so would be stylistically poor. But consider...
1: The chair was too small, too awkwardly positioned, and too fragile for him to sit on it.
2: John lived too far across on the other side of town for me to visit [him].
3: The estate where John lived was too far across on the other side of town for me to visit him [as often as I would have liked].
The longer the intervening text between the original mention of the "main" subject and its subsequent reference as an indirect object in an "adverb of purpose", AND the more complex the overall syntactic structure of the containing utterance, the more stylistically preferable it becomes to "re-reference" that subject/object.
It's really just a courtesy to the reader to assist in parsing, but it's not "invalid" to include it in shorter, simpler utterances.
Note that it's always possible for #3 above to be spoken by John's ex-wife, who lost the custody battle for their children. In which case it might be...
...too far ... for me to visit my children as often as I'd have liked
...and it would be the height of insanity to suggest that for syntactic reasons she's obliged to give the impression she wanted to visit her ex rather than her children!
It does seem at first glance that the question rotates around resumptive pronouns, but there is a grammatical distinction that we have to take note of before pounding the gavel.
The version without the pronoun has something called a gap. Gaps (also called traces) are blanks, or empty elements, in places where you would generally expect overt phrases. Like when a transitive verb or preposition is followed by nothing. They appear in two relevant constructions, which CGEL (2002) calls:
Relative clauses, finite or non-finite, freely modify nouns or nominals:
(1) a person [who(m) I trust ___] — a finite relative clause
(2) a framework [within which to place an observation ___] — a non-finite relative clause
Hollow clauses, however, don't do that. They don't have to be dependents of nouns, and they usually have to be brought to life by some specific phrase, a direct or indirect licensor:
(3) The chair was too small [for him to sit on ___]. — too serves as an indirect licensor of the hollow clause
(4) *This chair was small [for him to sit on ___]. — without a suitable licensor, adding a hollow clause renders the sentence ungrammatical
That means that hollow clauses are usually complements rather than modifiers, in contrast to relative clauses. So there are similarities and there are differences.
With this distinction in mind, let's now turn to CGEL itself. Discussing hollow clauses, it notes:
These items [too, enough, sufficient(ly)] also license ordinary infinitivals.
This is an important point I will illustrate below. (Their examples of both hollow and non-hollow infinitivals as indirect complements of these words are found on p. 1262, if you want to look.)
Let's turn to COCA for some examples.
(5) The lettering was too small for him to read easily...
Here, the object of read is a gap (=is absent), but we understand it to refer to lettering. Note that lettering itself is not an object; it's just a word that lends its semantic content to the gap. Every native speaker reads this as: "He couldn't read the lettering because the lettering was too small."
(6) At the time, his company was too small for him to receive unemployment benefits...
This sentence doesn't feature a hollow clause, however. If you got rid of the object of receive, the interpretation would have to do with him not being able to receive the company or something. But (6) of course means this: "He couldn't receive unemployment benefits because his company was too small at the time."
(7) Searching the sky, he spotted the thing, far away and too small for him to tell what it was...
Here, it is necessary with this wording. Because of certain constraints on extraction, you can't say this: *too small for him to tell what ___ was, although you can say this: too small for him to properly identify ___. You would have to reword it if you wanted extraction to work.
So as far as grammar is concerned, there is a free variation here: after too or enough, you can use either gapped or gappless constructions. Now, in OP's sentence, in contrast to (7), the pronoun is unnecessary, because 1) extraction is possible with this wording; 2) the pronoun refers to exactly the word that the gap would refer to. But it's not ungrammatical, because we can always choose between the two types of infinitivals after too. I'm on board with @FumbleFingers' intuition: this is a stylistically poor but syntactically correct sentence.
Resumptive pronouns are strictly ungrammatical in English. However, words like too and enough license both hollow clauses (which have gaps) and regular infinitival clauses (which don't). So the pronoun here is not resumptive to begin with; it is merely semantically redundant.
*The chair was too small for him to sit on it.
This is undoubtedly ungrammatical.
Pronouns used in place of a 'gap' in such clauses are known as 'resumptive pronouns'. In some languages they occur regularly in relative clauses, but in English they are ungrammatical, as evident from their inadmissibilty in simpler constructions like *"words which you may not understand them".
It depends in this particular case on the semantic focus of the utterance.
If his size is the issue, it's grammatical with it although it is not required:
The chair was too small for him to sit on it.
He needed a larger chair. If there is spoken emphasis on "him" it is referring to him in particular. For example, he's a big guy; the chair would have been fine for a person of average stature.
The chair was too small for him to sit on.
He needed a larger chair. With no spoken empahsis on "him."
If the chair's size is the semantic focus, then it's ungrammatical with it
The chair was too small for him to sit on
it
The chair was unsuitable for a man of his size, or it was too small for anyone but a child, say.
The chair was too small for him to sit on.
The complement varies according to the semantic focus.
And this, without "for him" complicating the issue, is ungrammatical:
The chair was too small to sit on
it.
to sit on a chair.
Ergo: The chair was too small to sit on. It was a child's chair.
to climb up a hill
to crawl down the wall [a bug for example]
to jump in the lake
to fly out of Chicago
All those verbs and prepositional phrases contain verbs and a preposition that are generally not separable. However, they are not phrasal verbs per se. This is true for action verbs (but also be: To be on the bus, What bus was he on?) followed by a prepositional phrase acting like a direct object. Those prepositional phrases receive the action of the verb.
Spoken language
What did he sit on? On a chair.
What did they climb up? A hill or a hummock?
What was the bug crawling down? Down the wall.
Where was the lake? Behind the house and he jumped in.
Where did they fly out of? Chicago.
You do not need to repeat the entire phrase.
The chair is to small for him to sit on it. is OK but in spoken English the it would not be used.
