"An Enquiry Concerning Human Understanding" is a philosophical work written by David Hume in the 18th century. It is one of the most influential works in Western philosophy and is considered a cornerstone of modern empiricism and skepticism.

In this book, Hume investigates the nature and limits of human knowledge, arguing that all knowledge is based on our experiences and observations of the world. He asserts that we cannot know anything beyond what we have observed or experienced, and that there is no rational basis for many of the beliefs that we hold.

Hume's philosophy is deeply skeptical, and he questions many of the traditional ideas of Western philosophy, including causation, induction, and the existence of God. He argues that our beliefs in these concepts are not based on reason, but rather on habit or custom, and that they cannot be rationally justified.

Hume also explores the nature of morality and human nature, arguing that moral judgments are based on sentiment rather than reason, and that human beings are fundamentally motivated by self-interest rather than by any innate moral principles.

Overall, "An Enquiry Concerning Human Understanding" is a profound and influential work that challenges many of the fundamental assumptions of Western philosophy. It is notable for its skepticism and empiricism, and for its rejection of many traditional metaphysical and theological concepts.