Download Lesson #4

Lesson #4
According to this theory, you can take a sentence and mathematically divide it into
parts.
Chomsky explains that phrase structure rules are basically "rewriting" rules. For
instance, a sentence can be rewritten as a noun phrase plus a verb phrase. In the
notation of transformational grammar, this rule is written as:
S --> NP + VP "a sentence consists of a noun phrase followed by a verb phrase"
A sentence can be further illustrated by a phrase structure tree, like this:
Starting with this base, we can begin to build rules which will allow us to generate an
infinite number of sentences.
Building a grammar
Our Goal: to build a grammar that generates all of the possible sentences of (English,
German, Swahili) and none of the impossible sentences.
Before we begin, we need to recognize that the individual words in a sentence are
organized into naturally coherent groups call constituents.
We've already looked at constituents in our activity on identifying subjects and
predicates. In these sentences, the subject and predicate are marked:
John snores.
Everyone likes the show.
A book lay on the table.
The dogs chased after the children.
Seen another way, the constituents in these sentences consist of a noun phrase (NP)
and a verb phrase (VP):
NP
John
Everyone
A book
The dogs
VP
snores
likes the show
lay on the table
chased after the children
The first rule we created above is S --> NP + VP "a sentence consists of a noun
phrase + a verb phrase". This rule can be illustrated in this chart:
S
NP
VP
John
Everyone
A book
snores
likes the show.
lay on the table.
chased after the
children.
The dogs
In the system of rules, S stands for Sentence, NP for Noun Phrase, VP for Verb
Phrase, Det for Determiner, Aux for Auxiliary (verb), N for Noun, and V for Verb
stem.
Look at the noun phrases in the examples. Some consist of a single noun (John,
everyone):
NP --> N "a noun phrase consists of a noun"
Others consist of an article (a, an) or a determiner (the) plus a noun:
NP --> Det + N "a noun phrase consists of a determiner plus a noun"
We're beginning to account for creativity and grammaticality judgments.
Let's look at verb phrases in the examples (pasted here again for your convenience):
S
NP
John
Everyone
A book
The dogs
VP
snores
likes the show.
lay on the table.
chased after the
children.
snores
|
V
VP --> V "a verb phrase consists of a verb"
likes the snow
| |
|
V Det N
VP --> V + NP "a verb phrase consists of a verb and a noun phrase"
NP --> Det + N ("the snow"), a rule we already created above
But the VP rule doesn't explain lay on the table or chased after the children. We need
a new VP rule to explain these phrases:
VP --> V + PP "a verb phrase consists of a verb and a prepositional phrase" (lay on
the table)
PP--> Prep + NP "a prepositional phrase consists of a preposition and a noun phrase"
(on the table)
NP --> Det + N "a noun phrase consists of a determiner and a noun" (the table)
With the rules we have so far...
S --> NP + VP
NP --> N
NP --> Det + N
VP --> V
VP --> V + NP
... we can generate sentences like...
The dog chased the
cat.
| | |
| |
Det N V
Det
N
...that we can illustrate in a phrase structure tree like...
... that are explained by these rules:
S --> NP + VP
NP --> Det + NP
NP --> N
VP --> V + NP