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Bertrand Russell’s Our Knowledge of the External World (1914) is an engaging book that investigates the problem of perception from an analytic-philosophical perspective. In it the great British mathematician and philosopher gives a thoughtful exposition of his logically motivated epistemology and argues for a controversial solution to a long-standing philosophical riddle. A dense and rich work, Our Knowledge of the External World is skilfully written with an accessible lucidity by a brilliant scholar. Requiring neither prior knowledge of logic nor aptitude for philosophical inquiry, the book serves as an essential reading for anyone interested in the intersection of logic and epistemology and in the development of analytic philosophy in the twentieth century. Aimed as an exhaustive treatment and following Russell’s earlier The Problems of Philosophy (1912), the book offers its readers a penetrating philosophical discussion on his theory of perception which, apart from demonstrating the immense pedagogical talent of its author, is regarded by many as embodying the scope (and limitations) of the analytic method in philosophy.
Bertrand Russell (1872–1970)—one of the greatest philosophers of the twentieth century—made noteworthy contributions not just to logic and philosophy but to a broad range of other subjects including education, history, political theory, and religious studies. He was born the grandson of Lord John Russell, who had twice served as Prime Minister under Queen Victoria, and was raised by his grandmother, Lady Russell. Having been educated privately, he entered Cambridge Trinity College in 1890, where he met Alfred North Whitehead and together started the ambitious project of reducing mathematics to logic. His early philosophical work (along with that of his pupil Ludwig Wittgenstein) had been mainly analytic and as such was one of the inspirations for the analytic movement in philosophy. Later in his life, however, Russell eventually lost sympathy with the very tradition he helped create.
The influential thinker who married four different wives led a life marked with controversy. Russell became publicly known already in 1902 with his popular essay “The Free Man’s Worship.” In 1907 he tried unsuccessfully to run for Parliament, campaigning for women’s suffrage and free trade, and in 1908 he was elected a fellow of the Royal Society. After World War I broke out, Russell took an active part in the No Conscription fellowship and was fined £110 for writing a leaflet that criticized a sentence of two years on a conscientious objector. As a result of his activities Trinity College deprived him of his lectureship in 1916, and when he was offered a post at Harvard University he was refused a passport. He also intended to give a course of lectures at the City University of New York (afterwards published in America as Political Ideals, 1918) but was prevented by the military authorities. In the same year he was sentenced to six months in prison for publishing a pacifistic article.
Further publicity came in the 1920s during which much of his work was written for the non-expert. Russell’s highly influential books were written with snide wit from a politically, morally, and intellectually left-wing radical point of view. During World War II, while having no permanent academic position, Russell was temporarily saved from poverty by a five-year contract to lecture at the Barnes Foundation in Pennsylvania, but the offer was withdrawn in 1943. He used his lectures as a basis for his History of Western Philosophy (1945), which became an immediate bestseller and was his main source of income for many years, as well as the reason for his Nobel Prize in literature (1950). On his return to Britain in 1944, Russell was reappointed lecturer and fellow of Trinity College. A fierce pacifist, Russell was also noted for his many spirited anti-nuclear protests in the years following World War II (one of which is the famous letter he and Einstein wrote against the bomb in 1955). He remained a prominent public figure until his death at the age of ninety-seven in 1970.
Russell’s Our Knowledge of the External World is concerned with the long-standing epistemological question about our relation, as perceivers of everyday phenomena, to the natural world around us, and the possibility of acquiring knowledge about it. Crudely speaking, the answer to this question divided modern philosophy into two main camps: Rationalists, such as Descartes, Leibniz, and Spinoza, believed that the natural world has a discernible structure to it, and that human beings, as perceivers of this world, have the ability to discern this structure and know it. Empiricists, such as Lock, Berkeley, and Hume, rejected this view. For them, Nature might have a certain structure to it, yet there was no way that we, human beings, could discern it or get to know it with certainty. Put in these terms, the rationalists seem to be claiming to know too much; and the empiricists—too little. It was only with the Kantian revolution that epistemology emerged out of the stalemate between rationalists and empiricists: According to Kant, what seems to be a discernible structure in natural phenomena is only imposed by us, as perceivers, on natural phenomena. Such imposition, moreover, is a necessary condition for any kind of perception to take place. Yet while Kant saved philosophy from eternal scepticism or sheer dogmatism, the price of his resolution was that “knowledge” was now more qualified than ever: If Kant is right, then we can only know how things appear to us, and there is no point in looking for knowledge of how things are “in themselves.”
For Russell, whose career shifted from embracing Kant to rejecting him, philosophy in the beginning of the twentieth century was for the first time in history coming into its own, thanks to the recent development in mathematical logic. One of the consequences of this development was that it allowed Russell to present a precise epistemological account of his view on our knowledge of the physical world using logical terms. Our Knowledge of the External World begins with a survey of the current tendencies. Emphasizing the role logic plays in the philosophical discourse, Russell continues to ask, as philosophers before him, can we come to know things about the physical world through the actions of our senses? And if so, how do we know these things? The answers he gives, however, are different both in style and in content.
As far as style is concerned, Russell saw his work in mathematical logic and its introduction into the philosophical method as one of his most important contribution to analytic philosophy. In Our Knowledge of the External World he restates the methodological shift he is bringing with him into the metaphysical discourse: “The function of logic in philosophy . . . is all-important. . . . [A]s applied to matters of experience, it is analytic rather than constructive; taken a priori, it shows the possibility of hitherto unsuspected alternatives more often than the impossibility of alternatives which seemed prima facie possible. Thus while it liberates imagination as to what the world may be, it refuses to legislate as to what the world is.” Moreover, not only does logic open an entire new perspective on philosophical questions, it also allows the philosopher to analyze concepts and ideas in far more rigorous ways than before. Such analysis appears in Our Knowledge of the External World, for example, in Russell’s discussion on perception in the chapter devoted to the continuum.
As for content, in both this book and in an article entitled “The Relation of Sense-Data to Physics” (also from 1914), Russell returns to the concept of sense-data, which he described earlier in The Problems of Philosophy, as a solution to the question “what is the object of perception?” According to Russell, sense-data are the (alleged) mind-dependent objects that we are directly aware of in perception, and that have exactly the properties they appear to have. For instance, upon viewing a tomato in normal conditions, one forms an image of the tomato in one’s mind. This image is red and round. This mental image is an example of a ‘sense datum.’
Sense-data are thus the characteristics and qualities we primitively, immediately sense about physical objects: color, shape, texture, temperature, and so forth. Previously, Russell had argued that sense-data were causal functions of physical objects. In other words, physical objects cause sense-data, which we then perceive when we exercise our five senses. A tomato exists in the real, physical world, and from that tomato we sense redness, softness, and roundness. The problem with this theory, however, is that we are only acquainted with the sense-data of redness, softness, and roundness—we infer that a tomato is causing these things, but we cannot know for sure that such a thing exists.
What Russell does in Our Knowledge of the External World, with the aid of his logical atomism (the theory that through rigorous and exacting analysis, language—like physical matter—can be broken down into smaller constituent parts) is to argue that “whenever possible, logical constructions are to be substituted for inferred entities.” With this in mind, Russell executes a kind of turnabout. Instead of saying that physical objects cause sense-data, he turns matters upside down and argues that sense-data construct the physical object. Sense-data don’t just testify to the existence of physical objects, they essentially create the physical world. But what is the fate of the real world when no perceivers exist to “create” it with their sense-data? To answer this question Russell defends phenomenalism, the view that translates all physical statements to phenomenal statements about mental appearances. Under this view, sense-data create the natural world in tandem with what Russell calls “sensibilia.” Sensibilia are “unsensed sense-data”—that is, how an object appears when no one is perceiving it at a given moment. This accounts for an object’s continued existence in the absence of perceivers. An important consequence of this theory is the notion that sense-data are not simply images held in the mind but are instead the actual building blocks of physics. Thus, sense-data inhabit the public space of science as well as the private space of experience.
Russell’s phenomenalism and his theory of sense-data, whose roots can be found in British empiricists such as Locke and Berkeley and their “theory of ideas,” was developed further by the philosopher A. J. Ayer, and gave rise to the philosophical school of logical positivism, yet many philosophers have rejected it, either because they believe that perception gives us direct awareness of physical phenomena, rather than mere mental images, or because they believe that the mental phenomena involved in perception do not have the properties that appear to us (for instance, I might have a visual experience representing a red, round tomato, but my experience is not itself red or round). Defenders of sense-data have presented a variety of arguments for their view, appealing to such phenomena as perspectival variation, illusion, and hallucination. Critics of sense-data have objected to the theory’s commitment to mind-body dualism, its difficulty in locating sense-data in physical space, and its apparent commitment in some cases to sense-data that have indeterminate properties. As Donald Davidson, a famous contemporary philosopher, has put it, solving the riddle of perception by introducing mythological entities such as sense-data is simply replacing one mystery with another.
But the logical treatment of epistemology has proved far more consequential to Russell’s career, indeed to the entire western analytic tradition in philosophy, than it might had seemed when Our Knowledge of the External World was originally published. Earlier in his career Russell had adopted the view that every denoting phrase (for example, “Scott,” “blue,” “the number two,” “the golden mountain”) denoted, or referred to, an existing entity. In 1905, when his landmark article, “On Denoting,” was published, Russell had modified this extreme realism and had instead become convinced that denoting phrases need not possess a theoretical unity. While logically proper names (words such as “this” or “that” which refer to sensations of which an agent is immediately aware) do have referents associated with them, descriptive phrases (such as “the smallest number less than pi”) should be viewed as a collection of quantifiers (such as “all” and “some”) and propositional functions (such as “x is a number”). As such, they are not to be viewed as referring terms but, rather, as “incomplete symbols.” In other words, they should be viewed as symbols that take on meaning within appropriate contexts, but that are meaningless in isolation.
As Our Knowledge of the External World demonstrates, not only did this distinction between various logical forms allow Russell to explain important logical puzzles and ambiguities in natural language, but, more important, it had influenced his metaphysics, epistemology, and even his meta-philosophy. Ultimately, Russell saw the philosopher’s task as discovering a logically ideal language that will exhibit the true nature of the world in such a way that the speaker will not be misled by the casual surface structure of natural language.
The common view among philosophers today is that Russell’s theory of sense-data has led to a dead end, but it is also clear that Russell’s new methods cleared the way for a whole new generation of metaphysicians, epistemologists, and analytical philosophers. From an historical perspective, Our Knowledge of the External World is yet another example of Russell’s clear thinking and rigor which puts him at the top of the distinguished and short list of mathematicians-philosophers—a list that includes giants such as Gottlob Frege, Edmond Husserl, and Kurt Gödel—whose treatment of philosophical questions through logical and mathematical reasoning has, for better or worse, widened the gap between modern analytic philosophy and the traditional continental philosophy of the nineteenth century.
Amit Hagar is a philosopher of physics in the History and Philosophy of Science (HPS) department at Indiana University, Bloomington. He has a Ph.D. from the University of British Columbia, Vancouver, and his area of specialization is the conceptual foundations of modern physics.
Posted October 20, 2008
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