What name did C.S. Lewis use for his 1933 book of philosophical fiction?

C.S. Lewis used the title The Pilgrim’s Regress for his 1933 book of philosophical fiction.

The full title is The Pilgrim’s Regress: An Allegorical Apology for Christianity, Reason and Romanticism. Lewis wrote it after his conversion to Christianity and structured it as an allegorical journey. The protagonist, John, travels through a landscape representing competing ideas and spiritual positions.

The title deliberately echoes John Bunyan’s The Pilgrim’s Progress, a major Christian allegory first published in the seventeenth century. Lewis’s book is more explicitly concerned with modern intellectual movements, desire, reason, and Christian belief.

It is not one of the Narnia novels or the science-fiction books later grouped as the Space Trilogy. Lewis revised the work’s preface for a later edition because he believed some readers had misunderstood the allegory’s purpose.