William Ernest Johnson (1858-1931) was a renowned British logician and economist, andalso a fellow of King's College, Cambridge. Originally published in 1924, this book forms the third of a three-volume series by Johnson relating to 'the whole field of logic as ordinarily understood'. The series is widely regarded as Johnson's greatest achievement, making a significant contribution to the tradition of philosophical logic. This book will be of value to anyone with an interest in Johnson's theories, philosophy and the historical development of logic.