Is this noun phrase a constituent of the given sentence?

Question

For the sentence, 'I saw the new play by Smith last week' is the noun phrase consisting only of a proper noun 'Smith' a constituent of the sentence?

Instinctively I think that it is not a constituent, for it is already a part of the prepositional phrase 'by Smith' (which is a part of the noun phrase 'the new play by Smith', which in turn is a part of the verb phrase 'saw the new play by Smith', I believe). Additionally, I cannot move 'Smith' to any other part of the sentence grammatically:

(1) I Smith saw the new play by last week.

(2) I saw Smith the new play by last week.

(3) I saw the new play by last week Smith. and so on...

However, when I try these tests for constituency, I'm having difficulty telling if they're grammatical or not. They don't sound terribly wrong, but they don't sound very natural, either:

(4) It was Smith I saw the new play by last week.

(5) Whom did I see the new play by last week? Smith.

Thank you for your help!

This is my attempt at a tree, by the way.

                                        S
                                    /        \
                                   NP        VP
                                   |     /        \
                                   PN    VP       AdvP
                                  'I'   /    \'last week'
                                     Vt    NP  
                                   'saw' /    \ 
                                       Det    NP
                                      'the' /    \
                                           AP    NP
                                           |   /    \
                                           A  NC    PP
                                         'new''play' / \
                                                    P  NPR
                                                   'by' 'Smith'

Answer 1

A constituent is one or more words that functions as a group within a syntactic structure. For example "house" is a constituent of the NP "The house", because it is a part of that higher NP. "The house" is also a constituent of "sell the house!". In these examples, "house" is an immediate constituent of the NP, and "the house" is an immediate constituent of "sell the house". Usually, we speak of the dominance relations of the nodes, so that NP immediately dominates N, and VP immediately dominates NP (also V). "Immediately dominates" is a special case of "dominates", where "dominates" means "is above" (using the graphic metaphor).

Take the sentence "The old dog likes sleeping on the rug". S dominates every node in that sentence – S is ultimately at the top of the tree. S dominates the N which is realized as "rug". S dominates the NP "the rug". S dominates the PP "on the rug", and it dominates the VP "sleeping on the rug"; and so on.

Smith is a constituent in all of your sentences. Every word is a constituent of its sentence (there are some words that people just stick in the middle of sentences that are not part of those sentences, e.g. epenthetic "uh," or "like,").

The problem with your constituency test is that there is no rule that says "you can move any constituent to anywhere else" whereby unmovability to a position is evidence that something is not a constituent. Those tests at best work for determining if a string of two or more words are, together, a constituent.