Emily Elizabeth Constance Jones (1848-1922) was an English logician and contemporary of Bertrand Russell, as well as Mistress of Girton College, Cambridge. In this book, originally published in 1911, she argues for the existence of another fundamental law of thought to join the Law of Contradiction and the Law of Excluded Middle: the Law of Significant Assertion. This book will be of value to anyone with an interest in logic or in Jones’ work.