Davidson studied at Harvard, under Alfred North Whitehead, among others, and wrote a dissertation on Plato's Philebus. His interests at this time were mainly in the "history of ideas," broadly construed, but under the influence of W. V. Quine, whom he often credits as his mentor, he began to gradually turn toward the more rigorous methods and precise problems characteristic of analytic philosophy.
During the 1950s Davidson worked with Patrick Suppes on developing an experimental approach to Decision Theory. They concluded that it was not possible to isolate a subject's beliefs and preferences independently of one another, meaning there would always be multiple ways to analyze a person's actions in terms of what they wanted, or were trying to do, or valued. This result is comparable to Quine's thesis on the indeterminacy of translation, and figures significantly in much Davidson's later work on philosophy of mind.
His most noted work (see below) was published in a series of essays from the 1960s onward, moving successively through philosophy of action into philosophy of mind and philosophy of language, and dabbling occasionally in aesthetics, philosophical psychology, and the history of philosophy.
Davidson was widely travelled, and had a great range of interests he pursued with nearly boundless energy. He had a pilots license, played the piano, built radios, and was fond of mountain climbing and surfing. He was married three times (the last was to the philosopher Marcia Cavell). He served terms as president of both the Eastern and Western Divisions of the American Philosophical Association, and held positions at Stanford, Princeton, Harvard, Oxford, and the University of Chicago. From 1981 until his death he was at the University of California, Berkeley.
Davidson's most noted work began in the 1963 with an essay, Actions, Reasons and Causes, which attempted to refute the prevailing orthodox view, widely attributed to Wittgenstein, that an agent's reasons for acting cannot be the causes of his action. This view was held on the ground that causal laws must be precise and mechanistic, whereas explanation in terms of reasons is not. Davidson argued that the fact that the expression of a reason was not so precise, did not mean that the having of a reason counld not itself be a state capable of causally influencing behaviour. Several other essays pursue consequences of this view, and elaborate Davidson's theory of actions.
In Mental Events Davidson advanced a form of the "identity thesis" in the philsophy of mind: that mental events just are brain events, and that mental states are brain states. The previous difficulty with this view was that it did not seem feasible to give laws relating mental states--for example, "believing that the sky is blue," or "wanting a hamburger"--to patterns of neural firing in the brain. Davidson argued that such a reduction would not be necessary to an identity thesis: it is possible that each individual mental state or event just is the corresponding brain state or event, without there being laws relating kinds of mental states to kinds of brain states--such as those in the above example. It might be nice if we had such a theory, but the fact that we don't have one--even the fact that we could not possibly have such a reduction, if such is the case--does not entail that the mind is anything more than the brain. Hence Davidson called his position "anomalous monism": monism, because it claimed that only one substance was at issue in questions of mind and brain; anomalous (from a-, not, and nomos, law) because brain states and mental states could not be connected by laws.
In 1972 Davidson published Truth and Meaning, in which he argued that any learnable language must be statable in a finite form, even if it is capable of a theoretically infinite number of expressions--as we may assume that natural human languages are, at least in principle. If it could not be stated in a finite way than it could not be learned through a finite, empirical method such as the way humans learn their languages. It follows that it must be possible to give a theoretical semantics for any natural language which could give the meanings of an infinite number of sentences on the basis of a finite system of axioms. "Giving the meaning of a sentence", he further argued, was equivalent to stating its truth conditions. In sum, he proposed that it must be possible to distinguish a finite number of distinct grammatical features of a language, and for each of them explain its workings in such a way as to generate trivial (obviously correct) statements of the truth conditions of all the (infinitely many) sentences making use of that feature. That is, we can give a finite theory of meaning for a natural language; the test of its correctness is that it would generate (if applied to the language in which it was fomulated) all the sentences of the form "'p' is true if and only if p" ("'Snow is white' is true if and only if snow is white). (These are called T-sentences: Davidson derives the idea from Alfred Tarski.)
This work was originally delivered as the John Locke lecture at Oxford, and launched a large endeavour by many philosophers to develop Davidsonian semantical theories for natural language. Davidson himself contributed many details to such a theory, in essays on quotation, indirect discourse, and descriptions of action.
After the 1970s Davidson's philosophy of mind picked up influences from the work of Saul Kripke, Hilary Putnam, and Keith Donnellan, all of whom had proposed a number of troubling counter-examples to what can be generally described as "descriptivist" theories of content. These views, which roughly originate in Bertrand Russell's Theory of Descriptions (and perhaps in the younger Wittgenstein's Tractatus Logico-Philosophicus) held that the referent of a name--which object or person that name refers to--is determined by the beliefs a person holds about that object. Suppose I believe "Aristotle founded the Lyceum" and "Aristotle taught Alexander the Great." Whom are my beliefs about? Aristotle, obviously. But why? Russell would say that my beliefs are about whatever object makes the greatest number of them true. If two people taught Alexander, but only one founded the Lyceum, then my beliefs are about the one who did both. Kripke et. al. showed that this was not a tenable theory; and that in fact whom or what a person's beliefs were about was in large part (or entirely) a matter of how they had acquired those beliefs, and those names, and how if at all the use of those names could be traced "causally" from their oiginal referents to the current speaker.
(If someone would be generous enough, please trim that and remove useful bits to some related article on theories of reference and content)
Davidson picked up this theory, and his work in the 1980s dealt with the problems in relating first-person beliefs to second- and third-person beliefs. It seems that first person beliefs ("I am hungry") are acquired in very different ways from third person beliefs (someone else's belief, of me, that "He is hungry") How can it be that they have the same content?
(Someone who knows this stuff better should fill in the gaps I'm leaving.)
Davidson approached this question by connecting it with another one: how can two people have beliefs about the same external object? He offers, in answer, a picture of triangulation: Beliefs about oneself, beliefs about other people, and beliefs about the world come into existence jointly:
Many philosophers throughout history had, arguably, been tempted to reduce two of these kinds of belief and knowledge to the other one: Descartes and Hume though that the only knowledge we start with is self-knowledge. Some of the logical positivists, (and some would say Wittgenstein, or Wilfrid Sellars), held that we start with beliefs only about the external world. (And arguably Frierich Schelling and Emmanuel Levinas held that we start with beliefs only about other people). It is not possible, on Davidson's view, for a person to have only one of these three kinds of mental content; Anyone who has beliefs of one of the kinds must have beliefs of the other two kinds.
Davidson's essays are collected in three volumes: Essays on Actions and Events, Inquiries into Truth and Interpretation, and Subjective, Intersubjective, Objective. Two more volumes are (as of 2003) projected: Problems of Rationality and Language, Truth and History. His early work with Patrick Suppes was published in a (co-authored) book entitled Decision-Making: An Experimental Approach. With Gilbert Harman he edited two collections, Semantics of Natural Language and (?). The Library of Living Philosophers published The Philosophy of Donald Davidson in 1999, which contains an autobiography, bibliography, and critical essays by a number of contemporary philsoophers along with Davidson's replies. (Several other simlarly designed collection exist devoted to Davidson.)