Donald Davidson ranks as one of the most influential philosophers of the second half of the twentieth and beginning of the twenty-first century. Davidson was trained in the analytic tradition in philosophy, which traces its origins back to Gottlob Frege and Bertrand Russell and continues through the logical empiricists and W. V. Quine, who was Davidson's teacher when he was a graduate student. A central focus of this tradition is the nature of language, and some of Davidson's most significant and widely cited work is his contribution to methodological and substantive debates about fundamental matters in the philosophy of language. Davidson argues that the most fruitful way to answer the basic question “What is it for our words to mean what they do?” is to investigate theories of meaning that model the knowledge an interpreter possesses when she understands a speaker's utterances. His work on theories of meaning connects with problems in the metaphysics of mental concepts, and his arguments for the position he calls anomalous monism present one of the live options in contemporary philosophy of psychology; at the same time, Davidson's ideas about language and mind have a bearing on the nature of action, and since his earliest published work Davidson has been one of the seminal figures in contemporary action theory. From the complex ties that link these disparate writings there emerges, especially in Davidson's later work, a critique of traditional ideas about truth, scepticism and relativism, and the relation of subjectivity to objectivity.