The main proponents of logical positivism—Rudolf Carnap, Herbert Feigl, Philipp Frank, and Gustav Bergmann—all emigrated from Germany and Austria to the United States to escape Nazism. Their influence on American philosophy was profound, and, with various modifications, logical positivism was still a vital force on the American scene at the beginning of the 21st century. Naturalized epistemology
The philosophical psychology and philosophy of mind developed since the 1950s by the American philosopher Willard Van Orman Quine (1908–2000), known generally as naturalized epistemology, was influenced both by Russell’s work in logic and by logical positivism. Quine’s philosophy forms a comprehensive system that is scientistic, empiricist, and behaviourist (see behaviourism). Indeed, for Quine the basic task of an empiricist philosophy is simply to describe how our scientific theories about the world—as well as our prescientific, or intuitive, picture of it—are derived from experience. As he wrote:
The stimulation of his sensory receptors is all the evidence anybody has had to go on, ultimately, in arriving at his picture of the world. Why not just see how this construction really proceeds? Why not settle for psychology?
Although Quine shared the logical postivists’ scientism and empiricism, he crucially differed from them in rejecting the traditional analytic-synthetic distinction. For Quine this distinction is ill-founded because it is not required by any adequate psychological account of how scientific (or prescientific) theories are formulated. Quine’s views had an enormous impact on analytic philosophy, and until his death at the end of the century, he was generally regarded as the dominant figure in the movement. Identity theory, functionalism, and eliminative materialism
Logical positivism and naturalized epistemology were forms of materialism. Beginning about 1970, these approaches were applied to the human mind, giving rise to three general viewpoints: identity theory, functionalism, and eliminative materialism. Identity theory is the view that mental states are identical to physical states of the brain. According to functionalism, a particular mental state is any type of (physical) state that plays a certain causal role with respect to other mental and physical states. For example, pain can be functionally defined as any state that is an effect of events such as cuts and burns and that is a cause of mental states such as fear and behaviour, such as saying “Ouch!” Eliminative materialism is the view that the familiar categories of “folk psychology”—such as belief, intention, and desire—do not refer to anything real. In other words, there are no such things as beliefs, intentions, or desires; instead, there is simply neural activity in the brain. According to the eliminative materialist, a modern scientific account of the mind no more requires the categories of folk psychology than modern chemistry requires the discarded notion of phlogiston. A complete account of human mental experience can be achieved simply by describing how the brain operates. The informalist tradition
Generally speaking, philosophers in the informalist tradition viewed philosophy as an autonomous activity that should acknowledge the importance of logic and science but not treat either or both as models for dealing with conceptual problems. The 20th century witnessed the development of three such approaches, each of which had sustained influence: common-sense philosophy, ordinary-language philosophy, and speech-act theory. Common-sense philosophy
Originating as a reaction against the forms of idealism and skepticism that were prevalent in England at about the turn of the 20th century, the first major work of common-sense philosophy was Moore’s paper “A Defense of Common Sense” (1925). Against skepticism, Moore argued that he and other human beings have known many propositions about the world to be true with certainty. Among these propositions are: “The Earth has existed for many years” and “Many human beings have existed in the past and some still exist.” Because skepticism maintains that nobody knows any proposition to be true, it can be dismissed. Furthermore, because these propositions entail the existence of material objects, idealism, according to which the world is wholly mental, can also be rejected. Moore called this outlook “the common sense view of the world,” and he insisted that any philosophical system whose propositions contravene it can be rejected out of hand without further analysis. Ordinary-language philosophy
The two major proponents of ordinary-language philosophy were the English philosophers Gilbert Ryle (1900–76) and J.L. Austin (1911–60). Both held, though for different reasons, that philosophical problems frequently arise through a misuse or misunderstanding of ordinary speech. In The Concept of Mind (1949), Ryle argued that the traditional conception of the human mind—that it is an invisible ghostlike entity occupying a physical body—is based on what he called a “category mistake.” The mistake is to interpret the term mind as though it were analogous to the term body and thus to assume that both terms denote entities, one visible (body) and the other invisible (mind). His diagnosis of this error involved an elaborate description of how mental epithets actually work in ordinary speech. To speak of intelligence, for example, is to describe how human beings respond to certain kinds of problematic situations. Despite the behaviourist flavour of his analyses, Ryle insisted that he was not a behaviourist and that he was instead “charting the logical geography” of the mental concepts used in everyday life.
Austin’s emphasis was somewhat different. In a celebrated paper, “A Plea for Excuses” (1956), he explained that the appeal to ordinary language in philosophy should be regarded as the first word but not the last word. That is, one should be sensitive to the nuances of everyday speech in approaching conceptual problems, but in certain circumstances everyday speech can, and should, be augmented by technical concepts. According to the “first-word” principle, because certain distinctions have been drawn in ordinary language for eons—e.g., males from females, friends from enemies, and so forth—one can conclude not only that the drawing of such distinctions is essential to everyday life but also that such distinctions are more than merely verbal. They pick out, or discriminate, actual features of the world. Starting from this principle, Austin dealt with major philosophical difficulties, such as the problem of other minds, the nature of truth, and the nature of responsibility. Speech-act theory
Austin was also the creator of one of the most-original philosophical theories of the 20th century: speech-act theory. A speech act is an utterance that is grammatically similar to a statement but is neither true nor false, though it is perfectly meaningful. For example, the utterance “I do,” performed in the normal circumstances of marrying, is neither true nor false. It is not a statement but an action—a speech act—the primary effect of which is to complete the marriage ceremony. Similar considerations apply to utterances such as “I christen thee the Queen Elizabeth,” performed in the normal circumstances of christening a ship. Austin called such utterances “performatives” in order to indicate that, in making them, one is not only saying something but also doing something.
The theory of speech acts was, in effect, a profound criticism of the positivist thesis that every meaningful sentence is either true or false. The positivist view, according to Austin, embodies a “descriptive fallacy,” in the sense that it treats the descriptive function of language as primary and more or less ignores other functions. Austin’s account of speech acts was thus a corrective to that tendency.