Bushido, the Soul of Japan is Nitobe's effort to explain to Western readers the moral world of the samurai. Writing in English, he answers the question of where Japanese notions of right and wrong come from, arguing that without understanding feudalism and Bushido, the moral ideas of modern Japan remain a sealed volume.
He defines Bushido as the code of moral principles which the knights were required or instructed to observe. It was not a written code but an unwritten, organic growth of decades and centuries of military career, sanctioned by deed and impressed upon the heart rather than set down in any charter or statute.
Nitobe traces the sources of the code to Buddhism, which gave calm trust in fate and composure before death; to Shinto, which supplied loyalty to the sovereign and love of country; and to the ethical teachings of Confucius and Mencius, which furnished its precepts of human relations and conduct.
The heart of the book examines the cardinal virtues in turn: rectitude or justice as the firmest precept, courage exercised only in the cause of righteousness, benevolence, politeness, veracity, honor, and the duty of loyalty. He illustrates each with maxims, anecdotes, and comparisons drawn from both Japanese and European tradition.
Closing chapters consider the training of the samurai, self-control, the institutions of suicide and the sword, the position of woman, and finally whether Bushido is still alive. Nitobe holds that the conditions which bred chivalry have disappeared, yet its light still illuminates Japan's moral path, surviving its mother institution.