The processes that pose problems to PS grammar are:
- discontinuous constituents (Eg: particles)
- remote relationship (Eg: those of cases)
- concord phenomena
A phrase structure grammar is essentially a grammar of segmentation and categorization, it is a taxonomic model – a grammar of lists, an inventory of elements, and a class of sequences of elements. Although it is very strong in giving a structural description of the language, yet it is deficient in generative capacity. It is incapable of accounting for all the intuitions of native speakers. It accounts for intra-sentence constituent relations, such as active-passive, declarative-interrogative and affirmative-interrogative. It cannot adjunct, delete and permute. It can neither solve the ambiguities nor explicate all grammatical relations.
Despite its rules of inference, binarity and inflexibility, etc. a PS grammar runs into difficulties in describing syntactic structures of questions, negatives, passives, relatives, etc. easily. It fails to capture the deep meaning. It cannot discover the crucial notions, not can it prevent the assignment of false, ungrammatical structure.
PS rules are incapable of – except by having recourse to very arbitrary solutions -of accounting for the multiplicity of relations existing either between elements in the same sentence or between different sentences.
1. The police diverted the traffic.
2. The traffic was diverted by the police.
3. The traffic was diverted by a country road.
PS rules fail to show the relationship that connects 1 to 2. In sentence 2 by the police will be shown as a prepositional phrase consisting of a preposition, a determiner and a noun, and in sentence 3 by a country road too will be shown as a prepositional phrase (prep + NP). Thus, it would ignore semantic considerations and case relations.
PS grammar does not have the precision, simplicity, elegance, power, insight, and competence of the TG grammar. It would be very complex and cumbersome and clumsy with so many constraints.
Discontinuous constituents cannot be shown by PS rules. PS grammar treats constituents as continuous units. In English interrogatives, the auxiliary is placed before the subject NP but it is closely related to the verb.
Eg: Does the old man live near the river?
The close relationship between the verb and the particle, for example, call off, take off, etc., cannot be shown by PS rules. PS grammar cannot account for stylistic variations i.e, there are a number of adverbials that can be placed in different positions in a sentence. No PS rule can account for the variation.
Eg: John often goes there.
Often John goes there.
John goes there often.
There are many dependencies like number agreement, tense agreement, etc. which are to be stated in the rules.
Eg: I go there every day.
She goes there every day.
The PS rules being classificatory in nature will become too complex if they are used to account for all such dependencies.
PS grammar fails to account for the recursive process which is one of the most productive processes in a language. Recursion is the process by which we can go on joining sentences without any limitations. A sentence can be expanded again and again by embedding and conjoining or by adding more and more relative process. For example, This is the cat that killed the rat that ate the moult that lay in the tent that was put up in the field…