My teacher drew this diagram in the class. He seperated the sentence as NP and S2 but it doesn't seem true. Can somebody help me?
It's hard to tell from your picture, because some of the lines are not really visible. But I'm pretty sure your confusion comes from the fact that your teacher is wrong, in multiple, fundamental ways:
- [which belonged to the old sailor] is modifying (part of) the object NP. You saw [a gray horse which belonged to the old sailor]. So that S2 needs to be inside the NP, as a sibling of what it's modifying. That's the whole point of relative clauses, and, more generally, of modifiers. Your teacher seems to have drawn it as a sibling of the subject, which would mean you, not the horse you saw, belonged to the old sailor. It's also apparently a child of the outer sentence, which makes no sense—what component of the sentence is it supposed to be? This sounds like the part you're asking about, and you're right to ask, because it makes no sense.
- Even more fundamentally: that object NP (including the relative clause) needs to be inside the VP (traditionally, as the direct sibling of the V). Objects are arguments of verbs; arguments go inside the phrase. I'm not sure where your teacher has put it; it seems to be not even linked into the sentence at all, which is never right for anything.
- Even more fundamentally: [S NP-subj VP] is the basic starting point for what a sentence is, and your teacher seems to have missed even that, and left the VP (with nothing in it but a V) floating around unattached.
- [gray horse] is definitely not an AdjP. It acts noun-ish, not adjective-ish, and it clearly means a kind of horse, not a kind of gray, so it's some kind of projection of the head [N horse], not [Adj gray].
- [old sailor] has the exact same problem as [gray horse].
This is not theory-specific stuff; it's part of the basic pre-theoretic model of the simple (surface) structure of sentences that different theories try to explain and represent in different ways.
As a first approximation, try this:
- [S [NP [Pronoun I]] [VP [V saw] [NP [D a] [AP [A gray]] [N horse] [S [C which] [VP [V belonged] [PP [P to] [NP [D the] [AP [A old]] [N man]]]]
By the way, that diagram comes from the Syntax Tree Generator by Miles Shang; you can just go to the web page, paste a bracket-notation tree, and it gives you the equivalent graphical tree. There are dozens of such programs, so I'm not specifically endorsing this one; you might, e.g., prefer one that lets you drag things around in the tree instead of forcing you to get the brackets right.