 Stebbing’s conception of logic is made clear in the first and last two chapters of the book. Logical thinking is “directed” thinking, aimed at answering a question or solving a problem. As such it involves reasoning: identifying and articulating the premises by means of which, by valid argumentation, to arrive at relevant conclusions. Reasoning proceeds in accord with certain rules and exhibits certain forms of inference, and one of the tasks of logical theory is to articulate these rules and make explicit these forms of inference—as Aristotle first did in developing his theory of the syllogism. One reason that Stebbing included discussion of syllogistic theory was that the rules and forms are relatively simple, so that the dependence of the validity of an inference on its logical form, for example, could be more easily ascertained and elucidated. But she was also concerned to introduce modern logic. She explains the basic symbolism of Whitehead and Russell’s Principia Mathematica in chapter 8, for example, and the theory of relations in chapter 10. She does not give any systematic presentation of the predicate calculus, however. In keeping with her conception of directed thinking, her concern is primarily with explaining the various concepts and doctrines, such as the concept of a proposition and Russell’s theory of descriptions, which help us in understanding logical thinking and logical theory.