The study is an investigation of Interlanguage (IL) developmental sequences of the acquisition of some aspects of negation and interrogation in Arabic by English-speaking learners in a foreign- language context; (i.e. Britain). The thesis contains eight chapters. The first chapter discusses the purpose of this research and the reason for selecting the topic. Chapters two and three survey and discuss the relevant literature. This includes discussions of different approaches to Second Language Acquisition (SLA), of models and hypotheses which have been proposed concerning the nature of learners' language and the process of SLA; and of studies of variability in language, both in general and specifically in the field of SLA. In chapter four, we analyze the two structures which are to be investigated in the study. First, basic assumptions of Arabic are discussed. Then, a short, analysis of the form of each structure is presented in both languages (Arabic and English). In the course of the analysis other issues that, are essential for the understanding of the realization of the features in the two languages are discussed. Chapter five presents first the hypotheses concerning the constraints which may govern the learners' IL(s). The rest of the chapter provides details of the investigation. The subjects are described, the tasks outlined, and details of data collection are described. Finally the criteria used in assessing the learners' responses are discussed. In chapter six, the results of the analysis are presented. Chapter seven contains the discussion and interpretation of the results in relation to the hypotheses formulated. The final chapter, chapter eight, summarizes the findings of the study in regard to the hypotheses. It also discusses some of the broader implications of the results of the study. Some suggestions for further investigations are also made.