Pushdown stores and subscripts

Abstract

Various devices for the improvement of phrase structure grammars (PSG) have been suggested recently. In particular, the PSG model with a pushdown store (PSG/PDS) as described by V. Yngve, and the PSG with subscripts (PSG/S) as described by G. Harman are considered. It is contended that such devices, even if they may do away with some of the difficulties of PSG, do not contain sufficient generative power to produce the structurally complicated sentences that are generated by other grammars (e.g., of transformational type). The handling of multiple disco, Ltinuous constituents (DC) in PSG/PDS, as well as the use of deletion rules in PSG/S is examined and criticized. It is shown that the improvements on PSG will not allow the grammar to generate all the sentences of the language that a transformational grammar (TG) does; moreover, the improvements on PSG are obtained only at the cost of introducing too much power at the PS level, so that the improved grammars in some cases will exceed the requirem@nts of the description, i.e. generate non grammatical sentences.