Abstract: The thesis of scepticism is a thesis about the human condition: the view that we can know nothing, or that nothing is certain, or that everything is open to doubt. This book examines the sceptical thesis that we can know nothing about the physical world around us. The author argues that the sceptical thesis is motivated by a persistent philosophical problem that calls the very possibility of knowledge about the external world into question, and that the sceptical thesis is the only acceptable answer to this problem as traditionally posed.On the basis of a detailed analysis of the sceptical argument advanced by Descartes, Stroud discusses and criticizes responses to scepticism by a wide range of writers, including J. L. Austin, G. E. Moore, Kant, R. Carnap, and W. V. Quine. In this discussion, Stroud is concerned with the significance of philosophical scepticism in three different respects.Firstly, he shows philosophical scepticism to be significant as opposed to insignificant or unimportant: the philosophical study of knowledge is not an idle exercise, and the comforting popular belief that we already understand quite well how and why philosophical scepticism goes wrong is simply not true.Secondly, Stroud argues for the significance of philosophical scepticism by defending it against the charge that it is meaningless or incoherent or unintelligible, and in doing so aims to articulate as clearly as possible what exactly it does mean.Thirdly, and most importantly, Stroud argues that philosophical scepticism is significant in virtue of what it signifies, or indicates, or shows: even if the sceptical thesis turned out to be false, meant nothing, or not what it seemed to mean, the study of scepticism about the the world around us would still reveal something deep and important about human knowledge and human nature and the urge to understand them philosophically. One aim of the book is to investigate how and why this is so. Engaging in a philosophical reflection about our knowledge of the external world in this way, Stroud argues, can also reveal something about the nature of philosophical problems generally and about philosophy itself; studying the sources of the philosophical problem of scepticism can yield some degree of philosophical understanding or illumination even if we never arrive at something we can regard as a solution to that problem.

Keywords: J. L. Austin, R. Carnap, Descartes, External World, Kant, Knowledge, G. E. Moore, Philosophical Scepticism, significance, W. V. Quine