A priest leaves a manuscript that cannot be published while he is alive. A prisoner answers the claim that pride made him an atheist. A philosopher asks why ghosts wear clothes.

Religious doubt has a history, and the people who made it did not all mean the same thing by doubt.

In 100: A World History of Religious Doubt, Lovepreet Singh follows one hundred thinkers who questioned belief in God, religious authority or supernatural claims. The journey moves across ancient India, China and the Mediterranean, through medieval disputes and the upheavals of print, to modern debates in Africa, Asia, Europe and the Americas.

Meet Xenophanes, the Buddha, Wang Chong, Spinoza, Jean Meslier, David Hume, Charles Darwin, Bhagat Singh, Kwasi Wiredu and many others through the arguments they actually made. Some rejected gods. Some defended a creator while challenging scripture or priestly power. Others asked what human beings could honestly claim to know.

Each portrait explains a life, a central question and the writings through which that question survives. The book keeps the differences between its thinkers visible, including changes of mind and the difficulties of reading someone through a critic, a translation or a later retelling.

Written in clear adult English, this 402-page volume includes an author's note, a documentary prologue, one hundred individual portraits, a selected chronology, 524 source notes, further reading and indexes. It invites readers into the long, varied history of questioning what others called certain.