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Syntax 2: Phrase Structure Rules

Will Styler - LIGN 101

Today’s Plan

Phrase Structure Rules
Tree Planting

Last time, we talked about constituents

Noun Phrases
Verb Phrases
Prepositional Phrases

… and we realized that the world of syntax isn’t flat

(Neither is the rest of the world, damnit)

Now, let’s think a bit more about those structures

Phrase Structure Rules

We have intuitions about what can be inside a noun phrase in English…

The big, strong rhinoceros
*The big, quickly rhinoceros
*The strong, charged rhinoceros

Same thing with a prepositional phrase in English

I saw her outside the barn
*I saw her outside fall over
*I saw her outside beautiful

Even a verb phrase has constraints in English

I hugged the small kitten
*I small hugged the kitten
*I hugged gently the kitten (???)

And sentences definitely have rules in English

Sam sent Amanda to the store.
*Sent Sam Amanda to the store.
*Amanda Sam to the store sent.

Unless Yoda you are

So, English has rules about how phrases are built

… that sounds useful!

A good theory of syntax does two things

1: It can generate all of the sentences that speakers of a language think are grammatical
2: It will not generate sentences that speakers of a language think are ungrammatical

Today, we’ll talk about a very basic approach to this

HUGE DISCLAIMER

Syntax is huge
We are only teaching you a small part of it to handle a small number of sentences.
- The rules you will have do not suffice for most complex sentences
The handout shows the rules we will use.
- There are other sets. Trust nobody else, not even the book!
I’m going to be saying “Don’t worry about that” a lot this quarter!
Consider LIGN 101 syntax to be a teaser for LIGN 121, where you’ll get a bigger picture
- … and a different set of rules!

Phrase Structure Rules

Rules that describe the sub-elements which can form a given syntactic constituent
- … and their ordering
We’re going to talk in terms of “building trees”
- But really, we’re building sentences
Syntax trees are built from phrase structure rules!

Phrase structure rule format

X → Y Z
S → NP VP
- “A sentence is composed of an NP, followed by a VP”

Phrase structure rules are like building blocks of sentences

We build sentences by building chunks using PS rules
- Then combining them into the desired larger forms

A Note on Notation

We’re going to talk about NP, N’, and N
- These are three different things
NP (/ɛn pi/ or “Noun Phrase”)
N’ or N̄ (“N-Bar”, /ɛn bɑɹ/)
- N’ and N̄ are two ways of writing the same thing
N (“Noun”, /ɛn/)
The symbols → and -> mean the same thing

How do we build trees?

Building a phrase structure tree (Part 1)

Step 1: Find constituents and think about what kinds of phrases they are
- “Huh, this is a preposition. There’s gotta be a PP around here…”
Step 2: Start from S and move down the tree, stitching together according to our PS rules
- Some folks work up, starting from individual phrases
- The top node is always S

Building a phrase structure tree (Part 2)

Step 3: Check to make sure every branching obeys the phrase structure rules
- “OK, this is Rule 9, now rule 1 to 2, then here’s 11…”
Step 4: A beautiful tree will be grown!

Some tree-drawing rules

You always branch downwards
- If a branch is moving upwards, you’re doing it wrong
Lines should never cross
- They don’t need to. If you think they need to, you’re doing it wrong.
You will not need to do any three-way branching for LIGN 101
- Every branch will have either one or two connections down.
Some branches may have two words (but not on your homeworks!)
- Compounds or phrases without internal structure “Mai Tai” or “Will Styler” or “back up”
Use the Phrase Structure Rules we gave you on the handout.

ONLY USE THE PHRASE STRUCTURE RULES WE GIVE YOU ON THE HANDOUT

# Introduction to our English Phrase Stucture Rules

Noun Phrase Rules

Rule 1) NP -> DET N’

Rule 3) N’ -> N

Rule 1) NP -> DET N’

Rule 3) N’ -> N

… but what if there’s no determiner?

Rule 2) NP -> N’

Rule 3) N’ -> N

Rule 2) NP -> N’

Rule 3) N’ -> N

Rule 2) NP -> N’

Rule 3) N’ -> N

How do we deal with adjectives?

Rule 4) N’ -> ADJ N’

We can combine Rule 1, Rule 4, and Rule 3…

Rules 1, 3, 4

We can combine Rule 1, Rule 4, and Rule 3…

Rules 1, 3, 4

We can combine Rule 1, Rule 4, and Rule 3…

… Rule 4 is recursive!

The N’ contains another N’!
It can apply as many times as you need!

(… and so on)

What about prepositions? Linguists love prepositions!

## Rule 5: NP -> NP PP ## Rule 6: PP -> P NP

Rules 5 and 6

“Two computational linguists from San Diego”

Now, let’s make a sentence!

Rule 7: S -> NP VP

Rule 8: VP -> V

Rules 2, 3, 7, 8

Rule 10: VP -> V PP

Rules 2, 3, 6, 7, 10

But lots of verbs are transitive, and take a noun phrase as the object

Rule 9: VP -> V NP

Rules 1, 2, 3, 7, 9

… and we can bring old rules back in!

… and we can bring more old rules back in!

Maybe we want to modify the verbing…

Rule 11: VP -> VP PP

This one’s recursive too!

“Two computational linguists from San Diego walked into a bar”

But this works with all the stuff we’ve been doing…

Is this starting to feel familiar?

Drawing Syntax Trees is combining small elements to make bigger, fancier trees

Complementizers put sentences within sentences

Words like “that”, “when”, “if”, “while”, “as”, and more

Rule 7: S -> NP VP

Rule 12: VP -> V CP

Rule 13: CP -> C S

### “That allows you to drop a whole new sentence in there!!”

Rule 12: VP -> V CP and Rule 13: CP -> C S

… we can go deeper

… and this combines with everything we’ve been doing …

… and just keeps getting worse …

(Don’t worry, that last one was mostly just me having fun)

You’ll be doing much simpler trees on tests and homeworks

Do not be tempted by darkness

Where you attach things changes the meaning!

Be careful where you put your prepositional phrases!

There are multiple ‘legal’ places to attach a given prepositional phrase
… but where you attach prepositional phrases changes the meaning
Sometimes the difference is subtle, but often it isn’t!

You may think…

… but in reality …

Drawing Trees

### How do you draw phrase structure trees?

- Only Electronically!

- This makes for fewer scanning and legibility issues

- Pros tend to use LaTeX, but that’s fancy

- Or using a tool like http://ironcreek.net/phpsyntaxtree/

- You’ll need to use bracket notation for that

- It’s frustrating at first, but it does the job

- This is a friendly tool https://groverburger.github.io/sapling/

[.S [.NP [.NP [.DET The ] [.N' [.ADJ proud ] [.N' [.N baker ] ] ] ] [.PP [.P from ] [.NP [.N' [.N San Bernadino ] ] ] ] ] [.VP [.V loved ] [.CP [.C that ] [.S [.NP [.N' [.N people ] ] ] [.VP [.V cheered ] [.CP [.C as ] [.S [.NP [.N' [.N Will ] ] ] [.VP [.VP [.V ate ] [.NP [.NP [.DET the ] [.N' [.ADJ massive ] [.N' [.ADJ chocolate ] [.N' [.N cake ] ] ] ] ] [.PP [.P from ][.NP [.DET the ] [.N' [.ADJ new ] [.N' [.N bakery ] ] ] ] ] ] ][.PP [.P with ] [.NP [.DET his ] [.N' [.N wife ] ] ] ] ] ] ] ] ] ] ] ]