"An Essay Concerning Human Understanding" is a philosophical work written by John Locke in the late 17th century. It is one of the most influential works in the history of Western philosophy and is considered a cornerstone of modern empiricism.

In this book, Locke sets out to explore the nature and limits of human knowledge, arguing that all knowledge is derived from experience, either through our senses or through reflection on our own mental processes. He rejects the idea of innate ideas or knowledge that we are born with, instead proposing that the mind at birth is like a blank slate or "tabula rasa" that is gradually filled with knowledge through experience.

Locke also examines the nature of language and how it relates to our ability to reason and understand the world. He argues that language is essential for human thought and that it shapes the way we perceive and understand the world around us.

Another important aspect of Locke's philosophy is his theory of personal identity. He argues that our sense of self is not based on any underlying substance or soul, but rather on a continuity of consciousness and memory.

Overall, "An Essay Concerning Human Understanding" is a profound and influential work that continues to shape modern philosophical thought. It explores many of the fundamental questions about human knowledge and perception that still occupy philosophers today.