This combines two earlier books- Straight Thinking and How to Use Your Head. He tells the common mistakes we make in our thinking, how our prejudices affect our thinking, how we draw conclusions from limited evidence, how we draw faulty comparisons, etc. He reduces straight thinking to four simple steps (1) observation suggests a problem; (2) problem is defined and solution considered; (3) experiments are set up and observed; (4) conclusions are drawn on experiments or observations. From these four basic principles he develops his twelve rules for straight thinking.... Fairly elementary, but people who need this sort of book don't want profundity.