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LING 1 Lecture Notes - Lecture 6: Steven Pinker, Arbitrariness, Dick CavettExam

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Ling 1 - Introduction to the Study of Language, UCLA
Introduction to Language - Lecture Notes
Sentence Structure I: Syntactic Trees
Goal: What is the structure of sentences? A natural assumption is that sentences are mere strings of
words, with no special structure (this is what we call 'Hypothesis 1'). This assumption is incorrect,
however. We show that sentences have more structure than meets the eye: they are organized into
subgroups of words, which are called 'constituents'. Constituents have a tree-like structure, which has lead
linguists to represent sentences as syntactic trees (this is what we call 'Hypothesis 2'). The crucial
argument in favor of Hypothesis 2 and against Hypothesis 1 stems from certain tests (called 'constituency
tests'), in which a group of words is targeted by a certain operation to yield another sentence. If the
operation succeeds, and yields a grammatical sentence, the group of words in question behaves as a
natural unit, and is likely to be a 'constituent'. For instance in Mary will meet the President the words the
President can be moved as a unit to the beginning of the sentence, yielding The President, Mary will meet,
which is grammatical. We conclude that the President is a constituent. By contrast, if we attempt to move
to the beginning of the sentence the words meet the, the result is ungrammatical: *Meet the Mary will
President. This suggests that meet the is not a constituent. With this background in mind, we give an
account of structural ambiguities, i.e. cases in which a given string of words can be organized into two
distinct trees, with different meanings.
1 Sentences Have a Tree Structure
1.1 Two Hypotheses: Sentences have a flat structure vs. Sentences have a tree-like structure
Let us consider first two very simple sentences, as in (1)a-b:
(1) a. Mary will meet the President
b. Your friend will meet the President
The simplest assumption -one which will turn out to be incorrect- is that this sentence is a mere
juxtaposition of words. According to this hypothesis the sentence has a 'flat' structure, which does not give
any information besides the fact that certain words are contiguous to certain other words:
Hypothesis 1: Sentences are just strings of words and thus have a 'flat' structure'.

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Ling 1 - Introduction to the Study of Language, UCLA
Linguistic analysis yields the conclusion that this initial hypothesis is incorrect, and that in fact sentences
have a 'tree-like' structure. Words are grouped together into sub-trees, which in turn are grouped into
larger sub-trees, etc. This view is illustrated below, without justification. We will motivate the particular
tree structure we have posited in the next section but the basic idea is this: a subtree can behave as a
single chunk, a single unit composed of several words).
Hypothesis 2: Sentences have a tree-like structure: words are organized into constituents (=sub-
(2) A B
Let us say that two words or groups of words 'form a constituent' if there is a sub-tree that contains them
and nothing else (we could have said just as well that they 'form a sub-tree', since a constituent is nothing
but a sub-tree; linguists tend to prefer the word 'constituent', however). We can now make an important
observation about trees:
Two words or groups of words that 'form a constituent' are contiguous. But the converse is not true:
some words or groups of words which are contiguous do not form a constituent.
For this reason a tree-like structure provides strictly more information than a 'flat' structure.
To be concrete, consider some examples:
-The words the and President are contiguous and form a constituent (which we call Z here). But meet and
the, although they are contiguous, do not form a constituent (there is no sub-tree that contains them and
nothing else; in fact the smallest sub-tree that contains them also contains the word President).

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Ling 1 - Introduction to the Study of Language, UCLA
-The words will and meet are contiguous, but they do not form a constituent; the smallest sub-tree that
contains both words is will meet the President, which also contains additional words (=the President) and
which we call X here. Hence there is no sub-tree that contains will and meet and nothing else. By contrast,
meet and the constituent the President form a constituent, which we call Y here, and are of course
contiguous as well (since whenever two words or groups of words form a constituent, they are
-In (1)b, friend and will are contiguous but do not form a constituent. By contrast, your and friend form a
constituent, and they are of course contiguous (since whenever two words or groups of words form a
constituent, they are contiguous).
Note: In traditional grammar, the sub-tree (=constituent) that comes to the immediate left of will is called
the subject of the sentence. The sub-tree (=constituent) that comes to the immediate right of meet is often
called the object, or the complement of the verb meet. While the terminology used in modern linguistics
is sometimes different, these are essential notions, which will be discussed in somewhat greater detail later
in the course.
Terminology: It will be useful in what follows to have some terminology to talk about trees and sub-
trees. The points that are joined by segments in a tree are called nodes. If a node N' belongs to a sub-tree
whose highest node is N, we say that N dominates N'. If N dominates N' and there are no intermediate
nodes between N and N', we say that N is the mother of N', and that N' is a daughter of N. If N is the
mother of N1 and N2, then N1 and N2 are sisters. (For future reference, we note that a 'branching node' is a
node that has at least 2 daughters; a node that has no daughter at all is called a 'terminal node'; and a node
that has 1 daughter is normally called 'non-branching).
1.2 Arguing for a tree structure: constituency tests
Why should we posit that sentences have a tree-like structure? Because certain groups of contiguous
words behave a natural units - for instance they may stand lone, be moved as a unit, be deleted as a unit,
or be replaced by a pronominal form. Other groups of contiguous words lack these properties, and appear
not to be natural units. The tree structure recapitulates the result of these observations, to which we now
Note: In each of the following, we put brackets around the words that appear to behave as a natural unit
(=as a constituent = as a sub-tree). Note that the information encoded in a tree can also be represented with
brackets (=put brackets around each group of words that form a sub-tree).
¨ Constituency Test 1: Ability to stand alone
(3) a. Mary will meet [the President]
b. Who will Mary meet?
-The President
the and President can stand alone as a unit; this suggests that they form a constituent.
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