Another factor, apart from Santayana's criticism, which stimulated the change in Russell's ethical thinking, was the impact of the First World War, which Russell passionately opposed. The war forced him to think afresh on a number of fundamental questions. For instance, Russell was forced to revise his views on human nature. As he says in his Autobiography , in his endeavour to understand popular feelings about war, he arrived at a view of human passions similar to that of psychoanalysts. Russell started believing that fundamental facts "in all ethical questions are feelings", (Russell 1917, 19) and that impulse has more effect in moulding human lives than conscious purpose.