Logic is about consistency - but not about all types of consistency. For example, if a man supports Arsenal one day and Spurs the next, then he is fickle but not necessarily illogical. If a legal system helps the rich but not the poor then it is unjust but not illogical. The type of consistency which concerns logicians is not loyalty or justice or sincerity, it is compatibility of beliefs. Logic, therefore, involves studying the situations in which a particular sentence is true or false, and the rules that determine whether a given argument is valid or invalid. Now fully revised and updated, Wilfrid Hodges' accessible study is the essential text for anyone who wants to learn about elementary logic. Assuming no previous knowledge of the subject, it takes the reader through the whole gamut of logical expressions, symbols and notations in a simple and lively way. Many helpful examples are given, and for readers who are mathematically adventurous there are optional sections introducing rather more challenging material. This new edition also contains some additional exercises, with updated sections on formalization and semantics.