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Double-based Transformations

A generative grammar of the type proposed by Chomsky makes use of two types of transformational rules- the singe-base or simple transformations, which is converting a sentence from one form to another, and the double- based or generalised transformations, which is combining two sentences to form a third. The two types of generalised transformations are- the conjoining transformation, which conjoins one sentence into another and the embedding transformation, which embed one sentence into another.

Coordination (Conjoining)

Coordination joins two sentence elements, called conjuncts. In a coordinate structure like cats and dogs, the conjunction coordinates the conjunct cats with the conjunct dogs. In many languages, conjunctions like and, or, etc. can conjoin words or phrases of virtually every category, under the condition that the categories being conjoined are of the same sort.

Two or more sentences are conjoined through coordinators like and but, through the use of the T-rules – Gapping and Repeated Structure Deletion.

My mother loved apples.
My mother loved oranges.

Coord -> My mother loved apples and my mother loved oranges.
Gapping -> My mother loved apples and oranges.
(Repeated structures are deleted.)

Coordination Transformation uses coordinating conjunction such as and or but to join strings together, however many strings there are.

Yudhishthira, Bhima, Arjuna, Nakula and Sahadeva married Panchali.

This sentence is derived from 5 simple strings, all conjoined by and.
Then, Repeated Structure Deletion deletes all the repeated structures in the long string.

John loves Mary and dislikes Susan.
He met a smart and beautiful girl.
I ought to and will write a good lesson.

Coordination is also possible for noun phrases as in the apples and the pears, verb phrases like run fast or jump high and adjectival phrases such as rich and very famous etc. There are two basic types of noun phrase conjunction, phrasal and sentential, based on the underlying P-marker from which each type derives. When phrasal conjunction is involved, the act denoted by the verb phrase is an act shared by the two or more persons or things denoted by the conjoined noun phrases. For example, when we have a sentence such as (1), the act of conferring one act is shared by the two persons who confer with each other.

(1) John and Mary conferred.

Sentence (1) cannot be paraphrased by sentence (2).

(2) John conferred and Mary conferred.

When sentential conjunction is involved, each person or thing denoted by the conjoined noun phrases has its act, as in (3).

(3) John and Mary know the answer.

That is, John’s knowing the answer and Mary’s knowing the answer are two distinct acts of knowing the answer; hence they cannot have a shared consciousness. Since two acts are involved, two underlying verb phrases are also involved, as indicated in (4), which is a paraphrase of (3).

(4) John knows the answer and Mary knows the answer.

Sentence (4) is derived by coordinate recursion from the underlying sentences (5) and (6).

(5) John knows the answer.
(6) Mary knows the answer.

In sentential conjunction, as its name implies, we start with two or more separate sentences, which are conjoined as in (4), and then if the two verb phrases are identical to each other, the first of the two identical verb phrases is deleted, generating sentence (3). Since we are starting with two sentences, we are of course starting with two verb phrases, and each verb phrase denotes an act or event distinct from that denoted by the other verb phrase. The conjoining of (5) and (6) may be achieved by the use of a double based transformation or by the use of a recursive phrase structure rule. If a double based transformation is used, it must have a structural description that matches the non-terminal representation of sentences (5) and (6), and its structural change must specify that those two sentences will be joined by and as in (7).


X + NP1 + VP1 +Y

–> X + NP1 +VP1 + and + NP2 + VP2 +Y

X + NP2 + VP2 +Y

Since (7) matches the non-terminal representation of (5) and (6), it will operate on these two sentences to combine them into one sentence (4). Then since the two verb phrases involved are identical, rule (8) will operate to delete the first of the two identical verb phrases.

(8) X+NP1+VP1+and+NP2+VP2+Y –> X+NP1+and+NP2+VP2+Y (VP1=VP2)

Applying rule (8) to sentence (4) will delete the first of the two identical verb phrases know the answer, transforming (4) into (3). The fact that there is only one verb phrase in (3) that is shared by the two noun phrases does not mean that (3) indicates phrasal conjunction. It is the number of the verb phrases in the underlying structure that indicates the number of acts involved, and since there are two verb phrases involved before the application of the rule (8), there are two distinct acts of knowing the answer is involved. Therefore, sentence (3) indicates sentential conjunction, even though only one verb phrase is left over.

The sentence Kim ran and jumped, in which two sentences are conjoined, has the same interpretation as the coordination Kim ran and Kim jumped, in which two sentences are conjoined. The dominant approach in generative syntactic theories indicates that phrasal coordination can be derived from sentential coordination using reduction rules. This approach states that Kim ran and jumped is the result of a reduction rule having deleted the subject of the second conjunct, Kim. Much syntactic research focuses on formulating appropriate reduction rules. This has turned out to be quite difficult due to the potential for phrasal constructions such as Kim and Sandy are similar, which lack a sentential source.