Phrase Structure by Edson Marín

Syntax: Phrase Structure Rules Linguistics 201

Syntax is the study of the arrangement of words into phrases and sentences. It attempts to describe at least two aspects of this phenomena. First, it describes which arrangements of words are grammatical, i.e. the well-formed ones. So it is concerned with characterizing the contrast below: (1)

a. The woman left town. b. * The left woman town.

(We use the convention of placing a “*” before strings of words that are not grammatical.) And second, it describes the relationship between the meaning that some particular group of words has and the arrangement of those words. So, for example, the actions carried out by Mary and Mark in the following are different, and this difference corresponds to the different position that these two words occupy in the sentence. (2)

a. b.

Mary kissed Mark. Mark kissed Mary.

Let’s begin with the first of these goals of syntax, the grammatical arrangements of words. At the bare minimum, we can observe that the linear order of words in English is important; we must find a means for describing which ordering of words is well-formed and which not. The simplest means of doing this is not available, i.e. we cannot merely list all the possible orderings of words. That is, we do not have stored in our heads a long list of possible sentences. The reason for this is simple: when we learn a new word, we know where that word may be positioned with respect to other words. For example, let me teach you a new word: stram. This is the name we shall give to a hair that grows out of one’s ear. Now that you know that word, you also know that the sentences below have the grammaticality values shown. (3)

a. That stram seems too short. b. * Stram that short too seems.

This fact shows that we cannot encode our knowledge of arrangements of words in terms of those words themselves. Instead we may make reference to the “categories” (or “parts of speech”) that those words belong to. This will correctly account for the fact that once we know that a word is a noun, we know automatically where it may fall in a sentence.

Syntax: Phrase Structure Rules Perhaps, then, we store in our heads all the grammatical arrangements of categories. This too cannot be correct; but for a more subtle reason. As the following examples illustrate, sentences may be of indefinite length. (4)

a. b. c. d.

Mary likes Mark. John said that Mary likes Mark. Sally believes that John said that Mary likes Mary. Sandy thought Sally believes that John said that Mary likes Mary.

Now it’s clear that a sentence of English cannot be infinitely long. But we need to determine whether this is a fact about our knowledge of the arrangement of words. That is, we need to figure out whether our knowledge of syntax allows infinitely long sentences or not. If our knowledge of syntax does not allow infinitely long sentences, then our model of this knowledge — the grammar we write — will have to reflect this fact. But this means in essence that we are going to have to decide at which point to terminate the expansion begun above. This termination point would have to be arbitrarily chosen, and this points to the inadequacy of supposing that our knowledge of syntax does not encompass infinite strings of words. In fact, the common conclusion from these observations is that the failure of our ability to utter infinitely long strings does not reflect some fact about our knowledge of syntax, but rather some aspect of our abilities in general. In particular, our life-span, or perhaps our limited memories or our good common sense, prevent us from uttering such things. Our knowledge of syntax does not. This distinction is described by saying that our linguistic “competence” is separate from our linguistic “performance.” But if our knowledge of which strings are grammatical and which aren’t includes knowledge about infinitely long strings, then we cannot possibly have such a list in our heads. Our brains are of finite size and therefore cannot hold things of infinite length. Hence we must find another means for representing our knowledge of the well-formed strings of words. A list is wrong. There must be some other way in which we recognize a string of words as a grammatical arrangement. There must be some way this knowledge is encoded in our minds that is finite, but still allows us to make a judgement about an infinite number of possible strings. We are going to set aside the solution to this problem for awhile, and discuss some other aspects of our knowledge of syntax. We shall encounter other problems whose solution will solve the problem just discussed. Consider the relationship between the following two sentences. (5)

a. b.

Mary has left. Has Mary left?

Linguistics 201 We know that these sentences are “related” in the following sense: they both mean the same thing, save that one is a question, the other a statement. More particularly, (5a) is uttered when the situation described by Mary has left is something the speaker wishes to assert. One would use this sentence, for instance, to convey the belief that the situation (5a) describes holds. We call such sentences “declaratives.” By contrast, (5b) is uttered when the speaker wishes to determine whether the situation described by Mary has left actually obtains. We call sentences of this sort “Yes/No Questions.” The important point is that the situation both of these sentences describe is precisely the same. The only difference is whether the speaker is asserting that the situation holds or seeking confirmation of it. This element of meaning is indicated by word-order. This is the fact that we need to capture. We need to fashion a theory that causes the words of these sentences to combine to describe the same situation, and correlate the difference in their word order with whether or not the sentence is a question or a declarative. This points back to the second goal of syntax: to account for the relation between the arrangements of words and their meanings. What we need to do in the case at hand is find a way of relating the word order differences in (5) to the difference in their meaning. The standard way of describing the relation between these sentences is to suppose that one is derived by a rule from the other. That is, one sentence is transformed into the other. In particular, we suppose that the question is “made of ” the statement plus the application of some transformation that moves around the constituents of the sentence to form the Verb-Subject word order. We don’t know yet how to characterize our knowledge that Mary has left means what it means and is a grammatical string of words (that’s what we left unfinished above), but let us suppose for this discussion that this aspect of our knowledge is given. So we begin with Mary has left, and now concentrate on the rule that yields Has Mary left?. It appears on the face of it that this rule interchanges the first two words. But this is not what the rule does, as the following pair of sentences indicates. (6)

a. The woman has left. b. * Woman the has left?

Perhaps what we should say, then, is that the first verb is moved to the front of the sentence. This is wrong as well, however, for two reasons. One of the reasons is sort of irrelevant for the present discussion; it has to do with sentences like: (7)

a. Mary left. b. * Left Mary?

What this example shows is that the rule will have to be constrained so that it moves only a certain class of verbs, and not so-called “main” verbs, verbs like left. 3

Syntax: Phrase Structure Rules The class of verbs that the rule moves is called “auxiliary” verbs (or, AUX). These verbs are: be, have, do and the modals: can, must, will, should, shall, could, would, etc. So the rule will have to be constrained so that it only moves Auxiliary verbs. English doesn’t have a way of forming Yes/No questions from sentences that don’t have Auxiliary verbs. The formulation of the rule cannot, as we suggested earlier, be simply: “Move the first auxiliary verb to the front of the sentence” because of examples like the following. (8)

a. The woman that has kissed Bill might leave. b. * Has the woman that kissed Bill might leave?

What we want is for the rule to produce (9) from (8a) instead. (9) Might the woman that has kissed Bill leave? What this example illustrates is that the notion “first auxiliary” is not what the rule makes reference to. The only way to get the rule to manipulate the right verb is to make reference to the collection of words that make up the subject. So our grammar must be able to make reference to groups of words. These groups are called “phrases”; and the subject of some sentence is the first Noun Phrase, a phrase that has a word of the category noun, in that sentence. We can now express the rule as follows. (10) Subject AUX Inversion Move the auxiliary verb that immediately follows the first NP to the front of the sentence. Now that we’ve established that phrases exist, we can rephrase our first task in the following way: what are the correct arrangements of words that make up some phrase. We can say that a Noun Phrase (NP) is made up of an initial determiner, then an adjective, then a noun, as in: (11) the brown fox We write a Phrase-Structure rule to describe this possibility, as follows: (12) NP → Det Adj N Note that though the noun is an obligatory part of a noun phrase, neither a determiner nor an adjective are. Thus, the following are possible noun phrases. (13)

a. b.

brown foxes foxes

To represent the optionality of the determiner and adjective, we’ll place these terms in parentheses; as in: 4

Linguistics 201 (14) NP → (Det) (Adj) N When more examples are considered, the rule that describes all possible arrangements of categories that make up a noun phrase looks something like: (15) NP → (Det) (Adj) N (PP) (CP) “Det” stands for “determiner,” a category that includes the, a, some, many, every, most and a few others. “Adj” stands for “adjective,” a category that includes blue, bad, happy, friendly and scores of others. We will come back to what these additional symbols represent.1 A sentence is made up of some NP followed by a collection of words that begins with a verb. This collection of words forms a phrase called a Verb Phrase, or VP, and is given by the following rules. (16) VP → V (NP) (PP) (CP) VP → AUX VP Some examples are: (17)

a. b. c.

eats eats the beans has eaten beans

And sentences themselves can have one of the two structures given below. (18) S → NP VP S → CP VP All the sentences we have seen up to now have the shape that the first of these rules describes: they are all sentences that start with a noun phrase and end with a verb phrase. But it is possible to have sentences that start with other sentences, this is what the “CP” is, as we shall see in a moment. An example of this kind is (19). (19) [CP That Mary hogs chocolate] bothers me. The “that Mary hogs chocolate” part of this sentence is a CP. Sometimes two rules of the sort in (18), which are identical up to one term, are abbreviated as follows: (20) S → 1

NP CP

And I should also warn you that the actual rules allow for tremendously more complex NPs than this simple start would lead one to expect.

Syntax: Phrase Structure Rules The “curly brackets” (i.e., “{” and “}”) should be understood as enclosing a list of options, exactly one of which must be chosen. Thus, (20) says that an S is made up of either an NP or a CP at the beginning, followed by a VP. The “PP” in these rules represents a group of words that contains a preposition, and forms a prepositional phrase. The following describes the shape that these phrases take. (21) PP → P

NP S

Some examples are: (22)

a. b. c. d. e. f.

on the table for the woman under the desk before the dance before Jerry left because Sally eats beans

We need one last phrase structure rule to be able to interpret all the phrases named by our present rules. This is the rule that yields “CP,” or “Complementizer Phrase,” as we shall call it. A CP is sort of like an S, except that it always has a “subordinating particle” or “complementizer” word at the beginning. So, for instance, in the following example, the group of words: that Peter left is just a sentence with the word that, a complementizer, at the beginning. (23) Mary said that Peter left. We have the following PS-rule, then: (24)

CP → C S

in which “C” stands for “Complementizer.” (Other complementizers are whether and if.) The phrases that words are arranged into, and that form sentences, can be represented graphically with what are called “Phrase-Marker Trees,” as in the following.

Linguistics 201 (25)

S NP

AUX

the

happy

child

has

VP V

eaten

apple

We are now able to solve the problem posed by the existence of infinitely long sentences. Because the rules we have written so far are â&#x20AC;&#x153;recursive,â&#x20AC;? they are able to generate infinitely long, and infinitely many, strings. The example of infinite length that we stumbled upon in (4) would be given the phrase marker tree representation in (26) with these rules. (26)

S NP

Sandy

thought

CP C that

S VP

NP N

Sally

believes

CP C that

S NP

John said. . . There is another context in which the infinity of English sentences can be seen, but this context calls for a change to the Phrase Structure rules we have so far developed. It is possible for English verb phrases to have an indefinite number of prepositional phrases in them, as in: (27) Mary walked [PP down the street] [PP over the hill] [PP through the woods] . . . . Presently, however, our rule for VPs allows only one PP. One way of using recur7

Syntax: Phrase Structure Rules sivity to capture these cases is to have two rules for VPs — one that introduces PPs (recursively), and the others to build VPs of the sorts that we have already seen. We might adopt something like (28), for instance. (28)

VP → VP PP VP → V (NP) (CP) VP → AUX VP

This will give (27) the phrase marker tree, or parse, in (29). (29)

S NP

Mary

VP VP

over D

walked down D

through D

the woods

the hill

the street Although the rules in (28) correctly allow for an indefinite number of Prepositional Phrases within a VPs, they aren’t quite right yet. They have the effect of putting PPs just at the right edge of a VP, and forcing all the other phrases that a VP contains to come to their left. Thus, for instance, they allow a Noun Phrase and a Prepositional Phrase to fit inside a VP as in (30), and not as in (31). (30)

S NP

Sam

met

at noon

Sally

Linguistics 201

(31) NP

Sam

at noon

Sally

met This is the correct outcome, as it turns out, since (31) is ungrammatical.2 But the rules in (28) say the same thing about PPs and CPs, and this is incorrect. Sentences such as (32) are perfectly grammatical. (32) I suggested [PP to Sam] [CP that he buy chocolate]. We need to change (28) therefore so that it allows CPs to follow PPs. It also turns out that there can be an indefinite number of CPs inside VPs, just as there can be an indefinite number of PPs. Thus, for instance, we find sentences such as: (33) Mary will dance [CP when Radiohead comes on] [CP if you ask her nicely] [CP which might be disturbing]. . . To describe both these facts, we can change the rules we have in (28) so that they also introduce CPs recursively, as in: (34) VP → VP PP VP → VP CP VP → V (NP) VP → AUX VP This will now give (32) the phrase marker representation in (35). 2

At least it’s usually judged ungrammatical by English speakers if the sentence is uttered with normal intonation.

Syntax: Phrase Structure Rules (35)

S NP

N I

VP V

NP that NP

suggested to

N Sam

VP V

he buy

NP N chocolate

So now we correctly allow either PPs or CPs to be the last phrase in a VP, but force NPs to precede a PP and/or a CP that they share a VP with. With these changes to the rules that characterize VPs, we are now able to describe the various ways in which VPs can be indefinitely long. Although there are still kinds of VPs that these rules do not describe, they describe enough of them for the purposes of this class. These will therefore be the rules for VPs that we will use. But some of our other rules will need to be further amended. We will want to make changes to the rule that characterizes NPs, because they also seem capable of having an indefinite number of PPs and CPs within them, as, for example, in: (36)

a. b.

a ball [PP on the table] [PP behind the picture] [PP near the stapler] . . . a ball [CP that you bought] [CP that Sally now has] [CP that might go to Bill] . . .

Here too we might consider using additional NP rules, one that recursively introduces PPs, one that recursively introduces CP, and another parallel to the one we fashioned earlier. (37) NP → NP PP NP → NP CP NP → (Det) (Adj) N The NP in (36a), for example, would consequently have the structure in (38).

Linguistics 201 (38)

NP PP

NP D

a ball on

behind N

near

P D

the stapler

the picture

the table But there is additional complexity to NPs that we do not see in VPs. This extra complexity arises because of the fact that adjectives too are capable of coming an indefinite number of times within NPs: (39) the big, unhappy, hairy, unattractive, . . . dog We will want to characterize this fact, like we have with PPs and CPs, by way of a recursive rule. But, unlike the PP and CP situations, we can’t rely on a rule like (40) because that will wrongly produce NPs like (41). (40) NP → Adj NP (41)

NP A unhappy

NP D

the

dog

What we need, here, is a phrase inside NPs that recursively introduces adjectives. This phrase is called an “N bar,” represented as N. We can use it to introduce PPs and CPs too — and, in fact, we will later encounter facts which suggest that this is correct. So, our rules building NPs will now look like this: (42)

NP → (D) N N→AN N → N PP N → N CP N→N

This will give to a noun phrase like (39) a phrase marker representation like that in (43). 11

Syntax: Phrase Structure Rules (43)

NP D

the

big

unhappy

hairy

N dog

And it will no longer give the NP in (36a) the representation in (38); but instead it will give in the structure in (44). (44)

NP D

N N

PP PP

on the table

near the stapler

behind the picture

ball There is another change we will need to make to our rules for NPs. This change is made necessary by the existence of the boldfaced noun phrases in (45). (45)

a. b. c.

Mary’s book has appeared. The woman’s book has appeared. The man from Spain’s book has appeared.

In these cases, there is another noun phrase found before a noun. This noun phrase has an “s” appended to the end of it, and is said to be in the “possession” relation to the noun. So, for example, in (45a), Mary is understood to “possess” the book; and similarly for the woman and the man from Spain in the (45b) and (45c). These noun phrases have the structures indicated in (46).

Linguistics 201 (46)

NP NP’s

Mary book b. NP NP’s

the

book

woman c.

NP NP’s D the

N N

PP P

man from

book NP N N

Spain Notice, incidentally, that the determiner, the, in the b and c examples, is part of the possessive noun phrase, and not part of the NP that contains it. That is, (45b) isn’t parsed as: (47)

NP D

NP’s

the

woman

N book

In fact, it appears that a noun phrase in English can start with a determiner, or it can start with a possessive NP, but it can’t start with both. We can discover this by first observing that certain kinds of noun phrases are prevented from starting 13

Syntax: Phrase Structure Rules with a determiner. NPs that have just a name in them, for instance, do not easily start with a determiner. This is indicated by the difference in the examples of (48). (48)

a. the woman b. * the Mary

Presumably this has something to do with the incompatible meanings of names and determiners. Whatever the cause, we can now see from the contrast in (49) that the determiner the must be within the possessive NP and not the larger one. (49)

a. the book b. * the Mary’s book

The goodness of (49a) shows that the can combine with book. Therefore, the badness of (49b) must be because the in this example is prevented from combining with book, and forced instead to be part of the possessive NP containing Mary, which (48b) has shown us isn’t good. These observations require that we change our NP rules so that they allow Noun Phrases to start with a possessive NP, but only when that NP doesn’t start with a determiner. This can be done by changing (42) to (50). (50) NP → (D) N NP → (NP’s) N N→AN N → N PP N → N CP N→N These rules now allow an NP to start with either a determiner or a possessive NP (both optionally). There is one last kind of sentence structure that we will consider and incorporate into our set of Phrase Structure rules: coordination. Coordination arises in cases, like (51), where the word or, and, or but brings together two strings of words (here in italics). (51)

a. b. c.

The man visited the woman or the child. The woman ran over the hill and through the woods. The child crawled home and ate chocolate.

One fact about this construction is that the “coordinator,” as we shall call the words or, and, and but, only brings together strings of words that fit our Phrase Structure rules. In the examples in (51), the strings of words make up an NP, in (51a), a PP in (51b) and a VP in (51c). If we try to join strings that don’t fit the rules which build phrases of these sorts, the result is ungrammatical, as in (52). 14

Linguistics 201 (52)

a. * The man visited the or woman the child. b. * The woman ran over and the hill through the woods. c. * The child crawled home and child ate chocolate.

Further, the strings of words that are found on either side of the coordinator must be the same kind of phrase. If the phrase to the right of and, for example, is a PP, then so must the phrase that shows up to the left of and. If the phrases on either side of the coordinator are not of the same kind, the result is ungrammatical, as in (53). (53)

a. * The man gave the book and to the woman. b. * The happy and child left town.

We can describe these facts with the following pseudo-phrase structure rule. (54) α → α coordinator α. Where α ranges over any category label (like Noun, Verb, etc.) or phrase (like NP, VP, etc.). This rule will now give (51a) the phrase marker representation in (55a), and (51c) the representation in (55b) below. (55)

S NP the man

VP NP

V visited

the woman b.

NP the child

S NP

the child

and

crawled

ate

home

chocolate

Syntax: Phrase Structure Rules This method of describing which arrangements of words (or more properly, categories) make grammatical English sentences has an interesting consequence. They specify how words are arranged linearly in terms of the way in which they are grouped into phrases. So, for instance, they say that sentences will be constructed in such a way that the string of words that starts the sentence can be grouped into a noun phrase and all of those words will precede the words that make up a verb phrase that ends the sentence. To be part of the noun phrase that starts a sentence a word must precede every word that is part of the verb phrase that ends that sentence. In a sense, the phrase structure rules can be thought of as a function from the grouping of words into phrases into their linear order. In certain cases, the phrase structure rules can group words in different ways, but yield the same linear ordering of those words. We say in these cases that the string of words is “structurally ambiguous.” To get a handle on cases of this sort, let’s begin by observing that the following string of words has more than one meaning. We say that it is “semantically ambiguous.” (56) The boy hit the elf on the table. This sentence can report that the elf on the table was hit by the boy, or it can report that the hitting of the elf by the boy took place on the table. Now, interestingly, this is one of those strings of words that can be given more than one groupings into phrases by our phrase structure rules — it is structurally ambiguous. Either the PP on the table can be parsed as part of the NP or not as part of the NP. It has the two representations given below. (57)

S VP

NP the boy

V hit

D the

N N N

PP P

elf on

the

N table

Linguistics 201 b.

S NP

the boy

VP V hit

NP D

the

elf

table

Is there a connection between this structural ambiguity and the meanings that this sentence carries? I wish to convince you that there is a connection and that the relationship between the various syntactic representations that this sentence has and its meanings is given by the following rule. (58) Modification Rule A PP modifies the phrase that it is a sister to. Îą and Î˛ are sisters if they are both dominated by exactly the same nodes in a phrase marker tree. This rule is a step towards completing the second goal of syntax that I outlined earlier: it describes one of the relations between the arrangements of words and the meanings they convey. It assigns to (57a) the first interpretation described above, the one in which it is the elf on the table which gets hit. And it assigns to (57b) the other interpretation, the one in which the hitting of the elf happens on the table. One reason for believing that there is a relationship between the structural ambiguity of the string above and its semantic ambiguity is because this hypothesis correctly predicts the number of meanings associated with strings of this sort. To see this, consider the following example. (59) I smashed the elf on the table with a hat. This sentence has five different meanings, depending on which phrase the PPs on the table and with a hat modify. We might expect more than this number of meanings as there are two PPs and three things that can be modified here: VP, the first NP and the second NP. But only five emerge. This is predicted by (58) since it makes the meanings that are available in cases like these dependent on the syntactic representations that our phrase structure rules allow. In (59), our rules permit only five different parses. They are: 17

Syntax: Phrase Structure Rules (60)

S NP

VP PP

VP V smashed

on the table

NP D

with a hat

the N elf on the table and with a hat both modify smashed the elf : “It’s on the table and with a hat that I smashed the elf.” (61)

S NP

VP NP

V smashed

D the

with a hat N

on the table

elf on the table modifies elf and with a hat modifies smashed the elf : “It’s with a hat that I smashed the elf that was on the table.”

Linguistics 201 (62)

S NP I

VP NP

V smashed

the

with a hat

on the table

elf on the table and with a hat both modify elf : “I smashed the elf that was on the table and had a hat.” (63)

S NP I

VP NP

V smashed

D the

N PP

N N

elf on

NP D the

N N

with a hat

table on the table modifies elf and with a hat modifies table: “I smashed the elf that’s on the table which has a hat (on it).”

Syntax: Phrase Structure Rules (64)

S NP

VP V

PP NP

smashed the elf on

NP D the

N N

with a hat

table on the table modifies smashed the elf and with a hat modifies table: “It’s on the table with a hat, I smashed the elf.” Consider, by way of contrast, the following example. (65) I smashed the elf on the table and with a hat. This sentence has only two meanings: that the elf is located on the table and has a hat, or that the smashing took place on the table and involved a hat. This is a direct consequence, again, of (58), because our phrase structure rules will permit only two parses of this string. Note here that we must have some understanding about how the PPs inside a conjoined PP modify. That is, our modification rule does not strictly speaking work in this example — what we need is some modification that talks about the special case that conjunctions are.