The name “positivism” comes from the writing of Auguste Comte, the 19th century philosopher of science and founder of sociology. In his Course of Positive Philosophy, published from 1830 through 1842, Comte described human history as progressing through three distinct stages which he called the theological, the metaphysical, and the positive — the final stage corresponding to the ordering of society by modern science. Comte’s positive philosophy was quite influential in the nineteenth century. According to Michel Bourdeau:
It is difficult today to appreciate the interest Comte’s thought enjoyed a century ago, for it has received almost no notice during the last five decades. Before the First World War, Comte’s movement was active nearly everywhere in the world. The best known case is that of Latin America: Brazil, which owes the motto on its flag ‘Ordem e Progresso’ (Order and Progress) to Comte and Mexico are two prominent examples. The positivists, i.e., the followers of Comte, were equally active in England, the United States and India. And in the case of Turkey, its modern secular character can be traced to Comte’s influence on the Young Turks.
Like Marxism, Comtean positivism heralded a new age — an age in which the superstition and religion of the past would be replaced by a society organized entirely upon scientific principles. Comte’s philosophy was less a philosophy of science than a social and political movement with a program for human progress. Unsurprisingly, it gradually turned itself into a sort of religion — with public worship services, a liturgy derived from Catholicism, and a calendar of positivist saints. The Comtean movement survived the century but was eventually extinguished by the First World War.
The logical positivism that emerged after the war, despite its lineage in the social and political enthusiasms of the previous century, was mainly an intellectual movement. It focused upon fundamental issues in the philosophy of science — to which it applied sophisticated modern analytical tools. This new positivism was primarily Germanic rather than French, and flourished in postwar Vienna and Berlin. It evolved out of a discussion group — the famous Vienna Circle — which included such figures as Moritz Schlick, Otto Neurath, Friedrich Waismann, Herbert Feigl, Gustav Bergmann, Victor Kraft, Hans Hahn, Karl Menger and Rudolf Carnap. Although they differed from each other in regard to the details, it was the common program of this group to provide an explication of modern science which distinguished it clearly from metaphysics, theology and ethics. Only science and mathematics, the positivists thought, provide knowledge.
Logical positivists emphasized the unity of the sciences, and as a consequence tended to be reductionists. They used the increasingly powerful logical and linguistic tools becoming available at the beginning of the century to illuminate both the connections between the individual sciences and the relationship between theory and observation. The positivists were empiricists, with antecedents in an empirical tradition that extended back through Ernst Mach and Bertrand Russell to David Hume. They eventually rejected any association with the philosophy of Comte and adopted the name “logical empiricism.” Many positivists subscribed to some form of phenomenalism. Rudolf Carnap, for instance, in The Logical Structure of the World, described the construction of the world out of what he called “elementary experiences”.
The most famous doctrine of logical positivism was probably the verifiability criterion of meaning, the contention that an assertion can be cognitively meaningful only if it can be empirically verified or is logically true. According to this criterion, the assertions of metaphysics, theology, and ethics are not wrong but without meaning. This claim is both sweeping and controversial. A common response has been to observe that the verifiability criterion involves a contradiction — that it, itself, is neither empirically verifiable nor logically true. Whether or not there might be some more nuanced formulation of the verifiability criterion that could render it cognitively meaningful is unclear.
Although often associated with the positivists, Karl Popper was not a member of the Vienna Circle and his idea of science differed from that of the positivists in important respects. He tended to downplay the role of induction and viewed science as being concerned primarily with refutation rather than confirmation. But Popper shared the positivists’ commitment to the epistemological priority of science, along with their conviction that there is a sharp bright line between science and non-science. Popper referred to the problem of distinguishing between science and non-science as the demarcation problem. He proposed a modification to the verifiability criterion which was directed toward demarcation, instead of meaning, and which relied upon the idea of falsifiability. It is this modification that is most commonly heard today, viz., that a claim or theory is scientifically meaningful only if it is empirically falsifiable. Popper’s approach managed to side-step the problem of induction and was somewhat less dismissive of non-science.
Three intellectual giants of the twentieth century explicitly rejected logical positivism. Kurt Gödel, a student of Hahn, was associated with the Vienna Circle as a young man but eventually broke with the movement and became a platonist. Albert Einstein was originally influenced by Mach, but after 1905 gradually asserted his own realist perspective — visible both in the general theory and in his refusal to accept quantum mechanics. In 1930, for instance, Einstein wrote to Schlick that “your presentation fails to correspond to my conceptual style insofar as I find your whole orientation, so to speak, too positivistic.” Palle Yourgrau, in A World Without Time: The Forgotten Legacy of Gödel and Einstein, strongly contrasts the later thought of both men to their positivist backgrounds. The situation with Ludwig Wittgenstein was more ambiguous. Wittgenstein was in intimate contact with the Vienna Circle, and his Tractatus was enthusiastically admired by many members of the group. In fact, the verifiability criterion likely originated in conversations between Wittgenstein, Schlick and Waismann. But the Tractatus already showed an underlying perspective that differed from positivism, and this difference only became magnified in Wittgenstein’s later thought. The treatment of language in the Philosophical Investigations formed a richer tapestry than anything in positivism — language being no longer connected to the world by simple empiricism. The positivist attire of the Tractatus might be what Wittgenstein had in mind when he remarked that, ”a picture held us captive.”
In the last half of the twentieth century, mainstream philosophy of science became increasingly critical of logical positivism. In 1951, W. V. O. Quine published an essay called “Two Dogmas of Empiricism,” which challenged the philosophical presuppositions of positivism. Quine made two main arguments: 1) He argued against the intelligibility of the analytic-synthetic distinction — a distinction that positivists had inherited from Kant, and which they needed in order to sort out the logical and empirical parts of scientific theories. 2) Quine also attacked the positivist doctrine of reductionism, arguing that the vehicle of meaning posited by the verifiability criterion is too narrow. “Our statements about the external world,” he said, “face the tribunal of sense experience not individually but only as a corporate body.” The resulting picture of scientific knowledge, according to Quine, is that:
The totality of our so-called knowledge or beliefs, from the most casual matters of geography and history to the profoundest laws of atomic physics or even of pure mathematics and logic, is a man-made fabric which impinges on experience only along the edges. Or, to change the figure, total science is like a field of force whose boundary conditions are experience. . .the total field is so underdetermined by its boundary conditions, experience, that there is much latitude of choice as to what statements to reevaluate in the light of any single contrary experience. No particular experiences are linked with any particular statements in the interior of the field, except indirectly through considerations of equilibrium affecting the field as a whole. . . If this view is right, it is misleading to speak of the empirical content of an individual statement — especially if it is a statement at all remote from the experiential periphery of the field.
Thomas S. Kuhn’s epochal The Structure of Scientific Revolutions was first published in 1962, in the positivist International Encyclopedia of Unified Science, edited by Neurath and Carnap. Kuhn’s book directed philosophical discussion away from the positivist program and toward a more concrete engagement with the history of science. In periods of scientific revolution, Kuhn argued, there is no empirical way to adjudicate between competing paradigms, implying that the contrast between metaphysics and science might be, at least, less stark than envisioned by positivism. “As the problems change,” Kuhn said, “so, often, does the standard that distinguishes a real scientific solution from a mere metaphysical speculation.” Since paradigm debates in science often lack a neutral observation language, they are characterized by the same “incompleteness of logical contact” that is found in metaphysical debates:
To the extent, as significant as it is incomplete, that two scientific schools disagree about what is a problem and what a solution, they will inevitably talk through each other when debating the relative merits of their respective paradigms. In the partially circular arguments that regularly result, each paradigm will be shown to satisfy more or less the criteria that it dictates for itself and to fall short of a few of those dictated by its opponent. There are other reasons, too, for the incompleteness of logical contact that consistently characterises paradigm debates. For example, since no paradigm ever solves all the problems it defines and since no two paradigms leave all the same problems unsolved, paradigm debates always involve the question: Which problems is it more significant to have solved? Like the issue of competing standards, that question of values can be answered only in terms of criteria that lie outside of normal science altogether, and it is that recourse to external criteria that most obviously makes paradigm debates revolutionary.
Gerald Holton’s Thematic Origins of Scientific Thought: Kepler to Einstein, published in 1973, illustrates the historical turn in the philosophy of science after Kuhn. Holton analyzed many examples of metaphysical “themata” that influenced the selection of scientific hypotheses — my personal favorite being the impact of Søren Kierkegaard on Niels Bohr’s formulation of the principle of complementarity. Other philosophers in the last half of the century, such as Paul Feyerabend and Imre Lakatos, took even more radical paths in their rejection of positivism, suggesting, for instance, that social and institutional factors frequently dominate empirical evidence. The Duhem-Quine thesis — the notion that a theory can withstand any single empirical falsification by making suitable adjustments in ancillary hypotheses — became something of a commonplace in the philosophy of science. In 1981, Hilary Putnam in Reason, Truth and History summarized the accumulated case against positivism, resuscitating the self-contradiction argument against the verifiability criterion. In the last analysis, Putnam claimed, no formal criterion can adequately capture scientific method:
Starting in the fifteenth century, and reaching a kind of peak in the seventeenth century, scientists and philosophers began to put forward a new set of methodological maxims. These maxims are not rigorous formal rules; they do require informal rationality, i.e. intelligence and common sense, to apply; but nevertheless they did and do shape scientific inquiry In short, there is a scientific method; but it presupposes prior notions of rationality.
The main attempt to rehabilitate logical positivism in recent years is probably Michael Friedman’s Reconsidering Logical Positivism, published in 1999. But even Friedman concedes that positivism today, “often serves more as an intellectual scapegoat than as an honorable philosophical opponent.”
Despite its reduced stature in the philosophy of science, logical positivism continued to play an important role in broader scientific and academic discussions. By mid-century, assisted by such sympathetic philosophers as A.J. Ayer and Karl Popper, positivism had become the dominant view of science in the English-speaking world. Its influence can be seen in the rise of behaviorism, in challenges (on the grounds of not being falsifiable) to psychoanalysis and Marxism, and in the increased use of experimental method in the social sciences. The falsifiability criterion has clearly prospered, and often crops up in debates over competing scientific hypotheses. Two recent examples of this are in the debate over anthropogenic global warming, in which both sides demand falsifiable predictions, and in the debate over string theory, in which critics suggest that perhaps string theory is not falsifiable. Scientists, even those with little patience for philosophy, have not surprisingly discovered the congeniality of the notion that science is the model for human knowledge, and the convenience of having a precise line of demarcation between science and non-science. As Rebecca Goldstein remarks, “For most scientists, this is all they need to know about the philosophy of science.”
The problem of demarcation has assumed an especially visible role in evolutionary biology. This is partly due to Popper’s suggestion, in his autobiography, that because natural selection is not testable, Darwinism is a “metaphysical research program” rather than a science. Popper subsequently retracted this suggestion and, as a consequence, is often cited both by biologists and proponents of intelligent design. I suspect that it is safe to say that Popper understood very well that evolution poses difficulties for the concept of falsifiability, and that he understood equally well that the theory of evolution is genuinely scientific. The underlying issue — which is ignored by the polemicists on both sides — is the adequacy of the criterion. Positivism was the creation of philosophers who were primarily concerned with the experimental hygiene of the physical sciences. But many modern biologists have resisted the “unification of the sciences” envisioned by positivism. Ernst Mayr, in Toward a New Philosophy of Biology (1988), for instance, adopts a modified reductionism; he accepts the “constitutive reduction” of biology to physics but rejects “explanatory reduction” and “theory reduction.” Mayr says that we must be willing to expand our concept of science:
Such a new philosophy of science will need to adopt a greatly enlarged vocabulary — one that includes such words as biopopulation, teleonomy, and program. It will have to abandon its loyalty to a rigid essentialism and determinism in favor of a broader recognition of stochastic processes, a pluralism of causes and effects, the hierarchical organization of much of nature, the emergence of unanticipated properties at higher hierarchical levels, the internal cohesion of complex systems, and many other concepts absent from — or at least neglected by — the classical philosophy of science.
Elizabeth A. Lloyd, in The Structure and Confirmation of Evolutionary Theory (1994), proposes that theory confirmation in the biological sciences be understood by the use of semantic models, as developed by Patrick Suppes, Frederick Suppe, and Bas van Fraassen. This approach is more complex, but would be more flexible than what is provided by the verifiability and falsifiability criteria.
Immanuel Kant remarked that two things filled him with awe, “the starry skies above and the moral law within.” Positivism, in essence, dismisses the latter; even were ethical norms universal, for positivists they would still be, qua moral laws, impossible to empirically verify — and hence without meaning. A. J. Ayer and C. L. Stevenson, probably the best known metaethicists working out of the positivist tradition, were ethical emotivists; they described ethical assertions as having no cognitive content, as being expressions of emotion — the assertion “Cruelty toward children is wrong,” for instance, merely expressing negative feelings about cruelty toward children. Other positivists, like Carnap, adopted a prescriptivist view of ethics, similar to that espoused by R. M. Hare; they described ethical assertions as being imperatives — so that “Cruelty toward children is wrong,” would be parsed as “Do not be cruel toward children.” The common thread in both cases is the notion that ethical assertions are fundamentally non-cognitive which is, in turn, a corollary of the positivist demand for verifiability. The general difficulty with non-cognitive theories, though, is that they cannot account for rational ethical discussion or moral persuasion. If non-cognitivism is correct, then there is no way to resolve moral disagreement — except through social pressure and coercion.
In a similar vein, logical positivism dismisses religious assertions as meaningless.
The solution to the demarcation problem, it seems to me, need not be as precise or formulaic as the positivists had supposed. Exact delineation might be the wrong idea. In a famous passage from the Investigations, Wittgenstein remarked that:
If I tell someone “Stand roughly here” — may not this explanation work perfectly? And cannot every other one fail too?
- Michel Bourdeau, “Auguste Comte”, Stanford Encyclopedia of Philosophy (2010). [↩]
- Bourdeau notes that Comte’s founding of the Religion of Humanity, in 1849, accomplished “a tour de force by uniting both believers and non-believers against him.” The theoretical justification for this direction was the “complete positivism” of the System of Positive Polity in 1851-1854, in which Comte argued that the claims of science should become subservient to “the continuous domination of the heart.” [↩]
- An excellent discussion of the history of the movement is John Passmore, “Logical Positivism“, The Encyclopedia of Philosophy 5 (New York: Macmillan, 1967), 52-57, [↩]
- Rudolf Carnap, The Logical Structure of the World, 1928, trans. Rolf George, 1967, U. of California, pp. 107ff. [↩]
- Thomas Uebel, “Vienna Circle”, Stanford Encyclopedia of Philosophy (2006). [↩]
- Letter from Einstein to Schlick, Nov. 28, 1930, cited in Gerald Holton, Thematic Origins of Scientific Thought: Kepler to Einstein (Boston: Harvard, 1973), 243. [↩]
- Palle Yourgrau, A World Without Time: The Forgotten Legacy of Gödel and Einstein (Basic Books, 2006). [↩]
- Uebel, “Vienna Circle”. [↩]
- Philip Shields, Logic and Sin in the Writings of Ludwig Wittgenstein (Chicago: U. of Chicago Press, 1993). [↩]
- W. V. O. Quine, From a Logical Point of View (Boston: Harvard, 1953), 20-46. [↩]
- Quine showed that attempts to explain analyticity by other notions, e.g., by synonomy, interchangeability salve veritate, or semantical rules, are circular; the other notions either presume analyticity or are as opaque themselves. Even though truth depends upon both language and extra-linguistic fact, Quine said, the assumption that there is some limiting case — purely linguistic truth — is “a metaphysical article of faith.” See Quine, 36. The consequence for Carnap is that, without the analytic-synthetic distinction, his distinction between empirical and logical frameworks, and hence between “internal” and “external” questions, cannot be satisfactorily explicated. See Rudolf Carnap, “Empiricism, Semantics, and Ontology”, Revue Internationale de Philosophie 4 (1950): 20-40. [↩]
- Quine, 43. [↩]
- Cf. Alexander Bird, “Thomas Kuhn”, The Stanford Encyclopedia. [↩]
- Thomas S. Kuhn, The Structure of Scientific Revolutions (Chicago: U. of Chicago, 1996) 3rd edition, Chapter IX. [↩]
- Holton, 144ff. [↩]
- Hilary Putnam, Reason, Truth and History (Cambridge: Cambridge University Press, 1981) self-contradiction argument: 105-113, citation:195. [↩]
- Michael Friedman, Reconsidering Logical Positivism (Cambridge: Cambridge University Press, 1999). [↩]
- William Briggs on AGW; Lee Smolin on string theory; Lubos Motl on falsifiability in physics. [↩]
- Rebecca Goldstein, “Falsifiability”, on the Edge World Question Center. [↩]
- Karl Popper, Unended Quest, Glasgow, 1976, p. 151. See John Wilkins, Darwin, evolution and Popper. [↩]
- Ernst Mayr, Toward a New Philosophy of Biology: Observations of an Evolutionist (Boston: Harvard University Press, 1988), 11. [↩]
- Ernst Mayr, 21. [↩]
- Elizabeth A. Lloyd, The Structure and Confirmation of Evolutionary Theory (Princeton N.J.: Princeton, 1994), chapter 2. Patrick Suppes, “A Comparison of the Meaning and Uses of Models in Mathematics and the Empirical Sciences”, Studies in the Methodology and Foundations of Science: Selected Papers from 1951 to 1969 (Dordrecht: Reidel, 1969), 10-23. Frederick Suppe, The Semantic Conception of Theories and Scientific Realism, (University of Illinois, 1989). Bas C. van Fraassen, The Scientific Image (Oxford: Oxford University Press, 1980). [↩]
- A. J. Ayer, Language, Truth and Logic, (New York: Dover, 1952). C. L. Stevenson, “The Emotive Meaning of Ethical Terms”, Mind 46 (1937), 14-31. This is sometimes called the “hurrah-boo” theory of ethics. [↩]
- R. M. Hare, The Language of Morals (Oxford: Oxford University Press, 1952). [↩]
- Ludwig Wittgenstein, Philosophical Investigations, trans. G.E.M. Anscombe, 3rd ed. (New York: Macmillan, 1958), 88. [↩]