This book aims to help college students to think critically about the kind of sustained, theoretical arguments which they commonly encounter in the course of their studies: arguments about the natural world, about society, about policy, about philosophy, and so on. The book expounds a novel method for handling such arguments and applies to reasoning expressed in natural language - has two distinctive features. It employs what is called the 'Assertibility Question', a key question in extracting and evaluating arguments, and it deals fully with the technique of 'suppositional reasoning', an important method of reasoning which is commonly ignored by writers in this field. The author applies the method to examples from a wide variety of sources. These range from newspaper articles to extracts from classic texts. There is a special chapter on scientific method and an appendix which explains some classical formal logic (a 'little light logic'). The book contains numerous exercises and concludes with carefully selected passages on which students can practise their critical thinking skills.