Hi. So in the last couple of videos, we've
talked about constituents, which are the
parts of a sentence, and we started
looking at syntactic rules. For example,
the fact that a noun phrase can be a
determiner and a noun. In this video,
we're going to make some more syntactic
rules, so then we can put all of them
together in a syntactic tree, because as
incredible and weird as it sounds
sentences in human languages are not
flat: they have hierarchical structure
within them, and that hierarchical
structure kind of looks like a tree. So in
the last video, we looked at some noun
phrases in English, and we came up with
this structure: a noun phrase is a
determiner and a noun, or a noun, or a
pronoun. These are all non terminals, and
then we have some non terminals like
DET pointing to terminals like the and a,
non-terminal pronoun, and an abstract
pronoun leading to terminal they I you,
and so forth. We could keep on going. So
we have noun phrases. We saw a little bit
of verb phrases. We'll look more at them
in a minute.
How about prepositions. Here we have some
phrases in English, above the town, above
Hanover, to the city, to Boston, on
September, on the fifth. So the one
interesting thing about the structure is
that it's a preposition plus a noun
phrase. If you can see sometimes what
follows the preposition is a determiner,
the, and then a noun like the town, and
sometimes it's just a noun, like Hanover.
So you always have a preposition, and a
noun phrase, and then you have the
structure of noun phrase that we studied
before. By doing this, you don't have to
redefine noun phrase for the specific
thing that goes through the prepositions.
You can just say that a prepositional
phrase is
a preposition plus this other thing you have
defined before. So in English you can
have the rule that a prepositional
phrase or a PP is a preposition plus a
noun phrase, and that an abstract
preposition is one of the terminals
above to, on and so forth. And we can
reuse the rule that we already had for
noun phrases, to put it inside of the
prepositional phrases. So this is one way
that we could describe prepositions in
English. This is very important. I keep
saying in English because rules are
dependent on the language. Languages have
different syntactic rules, obviously
because the languages have different
orders for their words. In English, we
have the preposition first, and then the
noun phrase, for example, to the city, to
Boston. In Japanese, we have the mirror
image of this. We have the noun first and
the preposition second. For example
machi e, to the city. Machi means city and
e means towards. Boston e is Boston to,
Boston towards. Kugatsu ni, September on.
Itsuka ni,
fifth on. So as you can see, these languages
are mirror images of one another. In
English, the rule for the prepositional
phrase is of the preposition and the
noun phrase. To Boston. In Japanese, the
rule is the mirror of English, noun
post-position. Kugatsu ni. Boston e. Machi e.
And of course English is also the mirror
image of Japanese. This happens in many
languages. Sometimes you can have the
preposition noun phrase, noun phrase
preposition. You can have
verb direct object, direct object verb.
For example, English. In English, you eat
pizza. In Japanese, you pizza eat, piza o
taberu. So the exact shape of the rules
will depend on what language you're
trying to parse with those rules. Let's
go back to English and let's say we have
the rules here. We have a prepositional
phrase, which has a preposition and a
noun phrase. We have the abstract
preposition which the non-terminal - which
leads to the terminal above, to, and on,
and we have rules similar to the ones
that we had. We had a noun phrase, which
has the non terminals determiner noun or
noun or pronoun, and we have the abstract
determiner non-terminal which goes to
the terminal. So we have the abstract
noun non-terminal which also to the
terminal town, Hanover, city, Boston
September 5th. So what would you do if
you wanted to draw the structure for
above the city? I'm gonna urge you to
give it a try. Pause the video, and try to
use these rules to draw the tree diagram
for the structure, for the prepositional
phrase above the city. And it means that
the PP rule would lead to some other
thing, and then those would lead to some
other thing, and then ... eternally. Give it a
try. Pause the video.
Let's check it out.
The first thing you would need to do,
because we know this is a prepositional
phrase, is start with a prepositional
phrase. As we have here. The second thing
is that you need - you need to know that
this above is a preposition and that the
city is a determiner and a noun, and the
one thing that we have that's a
determiner and a noun is a noun phrase. This
one here. So we need to go from
prepositional phrase to preposition noun
phrase. Here we will have the structures
that will fit above the city. The next
thing you would need to do would be to
change this non-terminal preposition
prep here, the P here, for one of our
actual terminals. For example, above. So if
the prepositional phrase is made up of a
preposition, which in this case is above,
and the noun phrase. What do we do next?
We have the city, and this is a
determiner and a noun. So a noun phrase
can go to a determiner and a noun. Noun
phrase, determiner, noun, noun phrase, determiner, noun. The next thing we would
need to do is to replace these non
terminals with the actual terminals that
we need. Determiner goes to the, and the
noun goes to city. Above the city. So you
can see, a prepositional phrase is - has a
preposition above, a noun phrase which
has a determiner the, and a noun the city.
Notice that this looks a little bit like
a tree in that it has branches that keep
on extending, and it tells us that
there's hierarchical structure to
sentences. For example when you have the
word above, above what? The city. So this
structure that is the sister to the word
above describe - tells you what is the
argument for this preposition, for this
function, if you will. Above what?
The sister, the city. Let's keep on going.
We have noun phrases, prepositional phrases.
Why not build a verb phrase? All these
are verb phrases: fly, prefer the morning,
leave Boston in the morning, leaving on
Thursday, and you might think, wait why -
those are not just verb phrases, they're
verb phrases plus something else. I'll
try to convince you that we can fit all
of this in a single verb phrase. What
rules do we need? First of all we could
have that a verb phrase in English is
described by - by a single verb, fly, by a
verb and a noun phrase, prefer the
morning, a verb a noun phrase and a
prepositional phrase, leave Boston in the
morning, or a verb and a prepositional
phrase, leaving on Thursday. You may think
that's really strange. Why would we fit
that? The reason is that the verb, and the
direct object have a relationship
between them, that is similar to a
preposition and a noun phrase. Remember
how we said above what? Above the city.
You're gonna say to Boston, to what?
Boston. We want the same kind of
structural configuration for verb
phrases. Prefer what? The morning. Leave
what? Boston. Leaving when? On Thursday. So
that these sisters to the verb will tell
you what are the important relationships
to the verb. So that's why we are
subsuming the noun phrase and the
prepositional phrase into a verbal
phrase, so that these objects, noun
phrases, prepositional phrases, can be
sisters to verb. And that way we can
answer rela - questions like, to prefer what? The
morning. To leave what? Boston. To be
leaving when? On Thursday, and so forth. We
have the same rules that we have before,
a prepositional phrase is the
preposition, and a noun phrase, and a noun
phrase is a determiner, a noun and a noun,
or a noun, and we have that an abstract
proposition goes to the - the terminals in
on. The determiner non-terminal goes to
the terminal the - the verb non-terminal
goes into terminal fly, prefer, leave.
Leaving the term - the non-terminal noun
goes through the terminals, morning, Bob,
Boston, Thursday. So now I present you
with a challenge. Please take out a piece
of paper, and try to draw the tree
structures for these four verb phrases,
using the rules that we have here, so
please pause the video and try to draw
the syntactic tree for these four verb
phrases. The first thing you would need
to do is have a verb phrase as your
origin node and then start drawing from
there. Please pause the video.
They would look something like this, in
the case of fly, is just a verbal phrase
which goes to a verb, which goes to the
terminal fly. Fly! I like it. You, fly. In
the second one, prefer the morning, we
have a verb phrase which is composed of
a verb a noun phrase, and the noun phrase
has a determiner the, and a noun morning.
Prefer, though, prefer what? The morning.
These are the trees for leave Boston in
the morning. A verbal phrase that has the
verb leave, leave what? The noun phrase
that goes to the noun, that goes to the
terminal Boston. Leave when? The
prepositional phrase that goes to the
preposition in to the noun phrase the
morning. So in when? The morning. Leave
what? Boston. And if you're taking LING 1,
at this moment you must be incredibly
confused, and be like why are we using
ternary structures and non binary
structures? I promise we'll get there.
Leaving on Thursday is a verb phrase,
leaving, I'm sorry, it has a verb leaving,
and then a prepositional phrase with a
preposition on Thursday. So we're leaving
when? On when? Thursday. So as you can see,
these relationships are the same level
of the rule. These relationships of two
sister nodes tell us that these two have
information that's related. So Boston is
related to leave, Thursday is related to
on, and so forth. That's why we say that
these have hierarchical structures,
because they organize themselves in ever
larger and larger information units, in
constituents. By the way, one piece of
evidence that verbs and noun phrases -
that verbs and direct objects form a
single constituent called a verb phrase
is idioms, phrases that have words but
mean something different than their
literal words, for example to bite the
bullet, or cutting corners, or getting a
second wind.
For example getting a second wind does
not mean that you got the second gust of
wind, it means that you got some more
life. To let the cat out of the bag means
to reveal a secret, it has nothing to do
with actual literal cats. So idioms are
structures where you have words,
but the idiom itself does not mean what
the literal words mean. It has an
additional supplementary meaning, for
example, to give someone the cold
shoulder does not mean that your
shoulder was - was cold, and the piece of
evidence that I want to present to you
is that idioms are usually combinations
of verbs and direct objects. There's
practically no idioms anywhere in the
world that are subject verb. What we
always find is verb and direct object,
which is a piece of evidence that tells
us that these two have a closer
relationship between themselves, and that
they should be in the same constituent.
Finally we can come up with a terminal
node, I'm sorry, with a - with, you know, a
macro node called sentence, which
connects everything that we have done.
For example, a sentence could be composed
of the subject and NP, and the verb, and
the direct object, VP, a verb phrase, and
then the verb phrase could be any of the
ones we proposed, a prepositional phrase
a noun phrase, and all of these. So with -
with the technique that we have so far,
you give it a try. Start with the node S
and then try to parse this sentence, and
then this one, and then this one. Take a
piece of paper, and give it a try. Pause
the video, and I'll count to five.
Welcome back. The tree for we
fly would be a sentence, which has a noun
phrase as its subject, which is composed
of a pronoun, when we have the terminal
we. It has a verbal phrase which is
composed of a verb with the terminal fly.
So what are we doing? Fly. Who is doing fly?
We. That's why these two are sister nodes.
So that would be the sent - that would be
the tree structure for the sentence We
fly. And as you can see, its hierarchical
relationships give us information about
who is doing what. A sentence - we start
with a sentence here, and then get to the
noun phrase - to a noun phrase for the
subject the students, the noun phrase has
a determiner the, and a noun students. The
sentence has a verbal phrase, prefer the
morning, and that verbal phrase has the
subcomponents verb, which has the
terminal prefer, NP which is the
direct object which has the elements
determiner, the noun morning. So what do
you prefer? The morning. Who prefers the
morning? The students. These hier -
these hierarchies in the tree gave you
information about which elements are
related to which, and what answers you
can add - yeah you can give using the
information in the questions, I'm sorry,
in the sentences. Finally, You leave
Boston in the morning. You have a subject,
a noun phrase, pronoun, you. What do you
leave? Boston in the morning, which has
the components leave, the noun phrase
Boston, and when did they leave Boston? In
the morning.
As a quick summary, what we've been doing
with the rules that we had before, we
have a very small context-free grammar
for English (That should have an extra m!0
with a few rules, as we have seen now, we
can describe the syntax of many English
sentences, and these rules form trees of
sentence parsing. As we have seen,
sentences aren't just flat string -
strings, they have a lot of internal
structure in them, and that structure can
tell us who did what when. For example,
and we will take full advantage of these
relationships. Rules are language
dependent. So your trees might look
different for different languages, so in
Japanese and English, they might be
mirror images of each other, but this is
fine. In the next couple of videos, we
will practice with context-free grammars.
