THE ACQUISITION OF LANGUAGE IS CONSIDERED AS A QUESTION OF SPECIFYING HOW CHILDREN'S CAPACITY FOR LANGUAGE INTERACTS WITH THEIR LINGUISTIC EXPERIENCE--THE INTERACTION TAKING THE FORM OF RELATING THE UNIVERSAL ASPECTS OF THE DEEP STRUCTURE TO THE IDIOSYNCRATIC ASPECTS OF THE SURFACE STRUCTURE OF LANGUAGE. THIS INTERACTION OCCURS IN THE ACQUISITION OF TRANSFORMATIONS. ONE QUESTION ARISING FROM THIS APPROACH IS WHETHER SOME OF THE LINGUISTIC UNIVERSALS SO RELATED EXIST BECAUSE THEY ARE UNIVERSALS OF HUMAN COGNITION. THE AUTHOR FEELS THAT STIMULUS-RESPONSE THEORIES DO NOT ACCOUNT FOR THE ACQUISITION OF DEEP STRUCTURES AND THAT A BIOLOGICAL APPROACH IS MORE APPROPRIATE. THE ORIGIN AND DEVELOPMENT OF CHILDREN'S GRAMMATICAL CLASSES IS DISCUSSED AND THE HYPOTHESIS IS DEVELOPED THAT GRAMMATICAL CLASSES "ARISE FROM AN INITIAL ASSIGNMENT OF SYNTACTIC FEATURES DERIVED FROM THE BASIC GRAMMATICAL RELATIONS." THE ACQUISITION OF TRANSFORMATIONS (ESPECIALLY NEGATION) IS ALSO DISCUSSED AND IT IS CONCLUDED THAT THEY REQUIRE "LITTLE OR NOTHING IN THE WAY OF OVERT PRACTICE." THIS ARTICLE WILL APPEAR AS A CHAPTER IN "GRAMMATICAL DEVELOPMENT IN CHILDREN," D.I. SLOBIN, EDITOR, ACADEMIC PRESS. IT ALSO APPEARED AS ONE OF SEVERAL RESEARCH REPORTS IN "STUDIES IN LANGUAGE AND LANGUAGE BEHAVIOR, PROGRESS REPORT V," SEPTEMBER 1, 1967, CENTER FOR RESEARCH ON LANGUAGE AND LANGUAGE BEHAVIOR, CITY CENTER BUILDING, 220 EAST HURON STREET, ANN ARBOR, MICHIGAN 48108. (AUTHOR/JD)