Lawyers perform many tasks. This book focuses on the core tasks with law. The core tasks are as follows: Structuring law Making law Interpreting law Using law in litigation and transactions, which involves two major tasks, namely applying law to facts and proving facts This book: examines the concepts of rationality and irrationality describes the reasoning processes that should underlie the core tasks that lawyers perform. These reasoning processes should ensure that each task is done as effectively and efficiently as human endeavour can make it. The main reasoning processes are as follows - conditional statement, deduction, induction, abduction, analogy, probability, policy, analysing ambiguity and observation. explains how an understanding of the reasoning processes that should be used becomes a basis for legal method since it is the basic for constructing models for working with law. However, it explains these only briefly since there is a full discussion of these models in a companion book Legal Method.