What is the number one? Does 2 plus 2 always equal 4? These seemingly simple questions have perplexed philosophers for eons, but the ideas of German philosopher Gottlob Frege (1848–1925) transformed the discussion. Frege believed that the truths of arithmetic and of all mathematics are derived from self-evident logical truths. His new way of looking at logic and mathematics was influential and his convictions revolutionized logic and laid the foundation for modern analytic philosophy. Joan Weiner presents an accurate, accessible explanation of Frege's ideas, tracing the development of his thought and making the essential concepts understandable.