IN ATTEMPTING TO DEFINE "SYNTACTIC VARIABLE," THE AUTHOR BASES HIS DISCUSSION ON THE ASSUMPTION THAT SYNTACTIC FACTS ARE A COLLECTION OF TWO TYPES OF RULES--CONTEXT-FREE PHRASE STRUCTURE RULES (GENERATING UNDERLYING OR DEEP PHRASE MARKERS) AND GRAMMATICAL TRANSFORMATIONS, WHICH MAP UNDERLYING PHRASE MARKERS ONTO SUPERFICIAL (OR SURFACE) PHRASE MARKERS. THE THESIS PRESENTS A SET OF CONSTRAINTS ON VARIABLES--UNIVERSAL AND LANGUAGE-PARTICULAR--AND DISCUSSES HOW THEY AFFECT SYNTACTIC RULES. HE POINTS OUT THAT CHOMSKY'S A-OVER-A PRINCIPLE IS BOTH TOO STRONG AND TOO WEAK, BECAUSE THE PRINCIPLE CANNOT BE EXTENDED TO ACCOUNT FOR THE PHENOMENA WHICH THE AUTHOR CALLS "SYNTACTIC ISLANDS." THE ENTIRE DISCUSSION CENTERS AROUND RULES AND CONSTRAINTS, WHICH ARE ACTUALLY LIMITS ON THE POWER OF VARIABLES THAT CAN APPEAR IN CERTAIN TYPES OF RULES. IT IS SHOWN THAT CONSTRAINTS, ESPECIALLY WITH THE NOTION OF "COMMAND," DIVIDE PHRASE MARKERS INTO "ISLANDS," SUGGESTING THAT THESE "ISLANDS" BEHAVE LIKE PSYCHOLINGUISTIC ENTITIES. THE AUTHOR PREFERS TO MAKE THE RELATIONSHIP BETWEEN GRAMMATICALITY AND ACCEPTABILITY MORE ABSTRACT THAN PREVIOUSLY ASSUMED BY TRANSFORMATIONALISTS. THIS THESIS WAS PREPARED AS PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY AT THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY. (FB)