The First Principles of Knowledge by John Rickaby, S.J. is a classic work of scholastic philosophy that offers a clear and systematic introduction to epistemology—the study of knowledge and its foundations. Written in the tradition of Thomistic thought, this work explores the essential questions of how we know, what we can know, and the principles that underlie all human understanding.

Rickaby, a distinguished Jesuit philosopher, presents a rigorous yet accessible examination of topics such as the certainty of knowledge, the reality of the external world, the nature of truth, and the reliability of human cognition. He carefully defends the position of moderate realism, affirming the objective reality of the world as it is known through the senses and reason, while addressing the errors of skepticism, idealism, and empiricism.