Describing phrase structure.
The TG linguist defines a phrase structure (
) as an ordered sequence of constituents (
).
Box one contains two formation rules in (1) and (2) to describe the calculus that in turn describes the linguist’s grammar. | The Languages of Science introduced the TG grammar as a calculus used by linguists in analyzing the components of the syntax of natural languages. We demonstrated there the way to use such a grammar to describe the syntax of some of the various calculi of logic. There and in previous chapters it was pointed out that one important way for the linguist to relate the calculi to each other is by the use of complex symbols and transformations. Presumably Chomsky first developed TG grammar as a tool for describing the sentences of a natural language. The analyst must keep in mind that it is the patterns and structures of English that constrain the form that the rules of the particular TG grammar take. This section introduces the tools of a TG grammar designed to describe the sentences, clauses, and phrases of both logical and natural languages. |
Describing phrase structure.The TG linguist defines a phrase structure () as an ordered sequence of constituents ().
Box one contains two formation rules in (1) and (2) to describe the calculus that in turn describes the linguist’s grammar. |
| The first rule in essence says that a constituent by itself is a phrase structure. The second rule says that a specific concatenation or ordered series of phrase structures is also itself a phrase structure. In accord with the second rule, suppose that (3) is a specific phrase structure of some fragment of English. It is often convenient to utilize tree graphs, i.e., tree diagrams for delineating phrase structure. The diagram is a tree graph where the concept of rewrite is represented by multiple vertically directed edges as in (4). It is particularly the large structures generated by the recursiveness in rules like the second rule for a phrase structure that motivate the use of tree diagrams for clarity. Later on in this book I have begun using a variant of this form, the one in (5), to represent phrase structures. Replacing both of these representations is an even more useful form — the one in (6). Computer scientists use this form to diagram constituencies. It is just one of many tools incorporated into the Unified Modelling Language (UML). |
Rules to describe syntactic structure.Now, the way to get from the formation rules to the phrase structure is by means of a set of phrase structure rule ( ).
These most generally have the form in (1) in box 2.
The structure characterized in (2) is generated by the PS-rule in (1).
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TG grammar has a replacement rule for interpreting the phrase structure rule, i.e. for deriving the structure from the rule.
This is a rule of inference, a replacement rule, a transformation of the metalanguage, which is the calculus for describing TG grammars.
The import of this rule is given in (2), the structure implied by the rule of (1).
Linguists may try to avoid the use of an environment structure, i.e. they make the  null.
The reason is that such a condition may usually be replaced by a suitable transformation.
Such rules as are free of this condition take the form described in box 3.
These are called “context-free rules.”
In an attempt to aid the student my choice has been to put labels for constituents in boxes of various colors.
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Abbreviating phrase structure rules.It is useful to abbreviate rules multiple rules with identical left sides and similar right sides. Normally the analysis would put parentheses around the elements that are optional. I have chosen instead to place a dashed box around such elements when placed in the maximally specified rule. The interpretation of such a rule is given in box 4. The rule in (1) for convenience is split onto two lines. |
| Similarly rules that diverge from each other on the right sides by having different elements may be placed in curly brackets. The interpretation of this kind of rule is given in box 5. Many rules may be abbreviated as one in a natural way using these devices. |
| The student should be aware that in presenting these last two principles, the first rule might have stated as equivalent each to two phrase structure rules. In this way the two statements about interpretation, which rule has already been given in box 3, would have been avoided. |
Backus-Naur form.A common variant of the Chomskyan form of the phrase structure rule is what is known as Backus-Naur form. This version adds a very useful device called a Kleene star, which allows the description of multiple occurrences of a constituent without the use of a (asyndetic) conjunction transformation. Box 6 tells how such a rule is to be interpreted. Notice that in this case the subscripts of each of the constituents do not simply indicate discreteness, but its 1) derivational and 2) sequential order. |
| The student should notice here that of the two uses of the Kleene star in (3) only the first one is illustrated in (1) and interpreted explicitly in (2). We’ll leave the second rule to be supplied as an exercise for the student. |
Unified Modeling Language.The Unified Modeling Language (UML) used by contemporary computer scientists has a way to diagram structure. Using this convention it is important to distinguish two ways in which structural constituents may be related. In the first case the relation between the two formal entities have a rhombus on the arrow end. This is the “has a” or the “is part of” relation. The corresponding relation in MultiNet is PARS, which we make PARTITIVE and relates concrete, ideal, or local objects. Our relation here connects formal entities. Each constituent is a distinct category that is interpreted as a part of some greater whole. |
| In the second case we use a triangle on the arrow end. This method indicates the alternative discrete realizations in a rule with curly brackets. This is the “is a (kind of)” or the “is realized by” relation. The corresponding relation in MultiNet is SUB0, which we make CLASS and relates entities to entities of the same sort on the intensional level. MultiNet does not allow an instance on the pre-extensional level to be a class. Our relation here connects formal entities but has the same kind of restriction when it comes to the initial category of phrase structure, which cannot be a (structural) class. Contextually these elements are thought of as different structures for the same kind of phrase describe by the conventions of box 5. |
