Orthodoxy (1908) is a book by G. K. Chesterton that has become a classic of Christian apologetics. Chesterton considered this book a companion to his other work, Heretics. In the book's preface Chesterton states the purpose is to "attempt an explanation, not of whether the Christian faith can be believed, but of how he personally has come to believe it." In it, Chesterton presents an original view of Christian religion. He sees it as the answer to natural human needs, the "answer to a riddle" in his own words, and not simply as an arbitrary truth received from somewhere outside the boundaries of human experience.
The book is developed as an intellectual quest by a spiritually curious person. While looking for the meaning of life he finds truth that uniquely fulfills human needs. This is the truth revealed in Christianity. Chesterton likens this discovery to a man setting off from the south coast of England, journeying for many days, only to arrive at Brighton, the point he originally left from. Such a man, he proposes, would see the wondrous place he grew up in with newly appreciative eyes. This is a common theme in Chesterton's works, and one which he gave fictional embodiment to in Manalive.
In keeping with this detachment from dogmatic religion, the book has few quotations from (although many allusions to) Scripture. It also lacks authoritative statements by religious authorities. To be sure, Chesterton is discussing the traditional orthodoxy, as contrasted with non-Christian ideas. He assumes his readers know its basic tenets well, as they are, he says, "sufficiently summarized in the Apostles' Creed". Chesterton is not investigating differences between Christians or details of their beliefs in a way that would require him to appeal to other authorities. Still, the book's message is mostly presented as a free intellectual inquiry by an individual looking for an explanation to the mysteries of human existence that satisfies his own innate reason.