TWO ASPECT MARKERS IN MANDARIN CHINESE ARE STUDIED WITHIN THE GENERAL FRAMEWORK OF A TRANSFORMATIONAL GRAMMAR. THEY ARE COMMONLY REPRESENTED AS "-LE," INDICATING COMPLETION OF ACTION, AND "-GUO," INDICATING THAT AN ACTION HAS TAKEN PLACE AT LEAST ONCE. THE PROBLEM INVOLVES SEVERAL SEEMING IRREGULARITIES IN THE FORMATION OF NEGATIVE SENTENCES AND THE SO-CALLED "A-NOT-A" QUESTIONS. THE SOLUTION PROPOSED CONSISTS OF THE IDENTIFICATION OF THE MORPH "-YOU" (AS IN MEIYOU) AND THE ASPECT MARKER "-LE" AS SUPPLETIVE ALTERNANTS OF THE SAME MORPHEME. A SET OF CONSTITUENT STRUCTURE RULES AND TRANSFORMATIONAL RULES ARE GIVEN. THE UNDERLYING P-MARKERS OF SEVERAL SENTENCES ARE ALSO GIVEN TO ILLUSTRATE THE RULES AS THEY RELATE TO THE PROBLEMS OF THE ASPECT MARKERS. (IT)