The title essay of this collection suggests Bertrand Russell’s lifelong preoccupation: the disentanglement, with ever-increasing precision, of what is subjective or intellectually cloudy from what is objective or capable of logical demonstration. The \ufb01rst \ufb01ve essays he calls ‘entirely popular’: they include two on the revolutionary changes in mathematics in the last hundred years, and one on the value of science in human culture. The last \ufb01ve, ‘somewhat more technical’, are concerned with particular problems of philosophy: the ultimate nature of matter, the connection between sense-data and physics, the problem of causality and di\ufb01erent ways of knowing. In these one can see the Russell method in operation, intellectual analysis dissecting the problem to its bare bones.