Christians have written expositions of their faith, from the apologetic works of the early Fathers to the great summas of medieval times, to modern treatises. Likewise Muslims have written many short and long expositions of their faith, from at least the 9th century until our own day; these are called by the Arabic word kalâm, meaning "discourse".

Christians and Muslims believe many things in common. They also hold that these beliefs have a rational foundation, since the preambles of faith can be proven by reason, and any teaching of faith which cannot be proven can at least be shown not to be self-contradictory or impossible. The arguments used in the Christian summas and the Muslim books of kalâm are highly philosophical, but guided by what each tradition holds as revelation. They are at the same time books of apologetic theology and philosophy of religion.

Christian and Muslim apologetic books normally begin with a section on the preambles of faith and then go on to show the unique validity of their own religion. There is literature enough on how each religion is distinct. This book is different. It attempts to let Christian and Muslim thought advance together as far as they can go.

This book is inspired particularly by St. Thomas Aquinas’ Summa contra gentiles, Books I-III. In spite of the title, it is not an attack on anyone or any religion. While the fourth volume — not included here — is a defence of the distinctive content of the Catholic faith, these first three of the four volumes of the work build carefully the shared vision held by Christians and Muslims alike. They bring supportive insight from Christian reflection which has been foundational for the development of Western culture. In the present developments of interchange between East and West these insights attained by reason in a context of deep faith can constitute a veritable treasure chest for Islamic thinkers as they build toward the future.

Why write another work then? First of all, it is necessary to update Thomas Aquinas, since many of his arguments and illustrations are based on the defective physical sciences of his day. Secondly, it is necessary to present his thought more simply for readers who would find it laborious to go through his complicated dialectic without familiarity with the careful structures of scholastic reasoning. Nevertheless, the reader will find this book fundamentally a reworking of the Summa contra gentiles and a summary of its main arguments. Thirdly, in this day of searching for shared vision as a basis for dialogue as cooperation rather than conflict between civilizations this work provides one of the most rich and ordered sources.

References after subtitles are to the books and chapters of Contra gentiles. Thomas’ custom was to conclude each section with a Biblical quotation that supported his argument. I do the same, adding quotations from the Qur’ân.