  Williams was almost alone in his time in holding not only that the problem does admit of a solution, but in presenting a novel solution of his own. To do this, he needed to argue against Hume, and Hume’s twentieth century successors Bertrand Russell and Karl Popper, who had declared the problem insoluble, and also against contemporaries such as P. F. Strawson and Paul Edwards, who had claimed that there was no real problem at all (Russell 1912, Chapter 6; Popper 1959; Edwards 1949, pp 141–163; Strawson 1952, pp 248–263). Williams tackled the problem head-on. In The Ground of Induction (1947) he makes original use of results already established in probability theory, whose significance for the problem of induction he was the first to appreciate. He treats inductive inference as a special case of the problem of validating sampling techniques. Among any population, that is, any class of similar items, there will be a definite proportion having any possible characteristic. For example, among the population of penguins, 100% will be birds, about 50% will be female, some 10%, perhaps, will be Emperor penguins, some 35%, perhaps, will be more than seven years old, and so on. This is the complexion of the population, with regard to femaleness, or whatever.