Alfred North Whitehead (1861–1947) was a prominent English mathematician and philosopher who co-authored the highly influential Principia Mathematica with Bertrand Russell. Originally published in 1919, and first republished in 1925 as this Second Edition, An Enquiry Concerning the Principles of Natural Knowledge ranks among Whitehead's most important works; forming a perspective on scientific observation that incorporated a complex view of experience, rather than prioritising the position of 'pure' sense data. Alongside companion volumes The Concept of Nature (1920) and The Principle of Relativity (1922), it created a framework for Whitehead's later metaphysical speculations. This is an important book that will be of value to anyone with an interest in the relationship between science and philosophy.