This paper surveys some issues that arise in the study of the syntax and semantics of natural languages (NL's) and have potential relevance to the automatic recognition, parsing, and translation of NL's. An attempt is made to take into account the fact that parsing is scarcely ever thought about with reference to syntax alone; semantic ulterior motives always underly the assignment of a syntactic structure to a sentence. First I con- sider the state of the art with respect to arguments about the language-theoretic complexity of NL's: whether NL's are regular sets, deterministic CFL's, CFL's, or whatever. While English still appears to be a CFL as far as I can tell, new arguments (some not yet published) appear to show for the first time that some languages are not CFL's. Next I consider the question of how semantic filtering affects the power of grammars. Then turn to a brief consideration of some syntactic proposals that employ more or less modest extensions of the power of context-free 1.

The varieties of mathematical basis for formalizing linguistic theories are more diverse than is commonly realized. For example, the later work of Zellig Harris might well suggest a formalization in terms of CATE-