BOOK V - Page 4

The Philosophy of Science

Popper’s philosophy comprehensively addresses the four functional topics of philosophy of science. His explicit rejection of the positivist and naturalistic philosophies of the seman­tics of language represents a basic problem shift, a reconceptualization of science as viewed by academic philosophy of science. 

Scientific Criticism

The central feature of Popper’s philosophy of science is his falsificationist criterion, as well as its consequent rejection of the naturalistic thesis of the semantics of language and redefinition of the concept of theory to mean any universally quantified statements.  Theories are conjectures that are created by the human imagination, and similarly the meanings associated with the theories’ constituent terms must also be created artifacts distinguished as world 3 objects.  The theories do not originate by any natural process such as induction, and similarly the constituent meanings are not determined by any natural process such as perception.  The theories are not permanently established by verification or confirmation, and similarly the meanings are not permanently established by virtue of any foundational ontology.  The logic of criticism is the modus tollens form of argument, in which a theory is falsified, if the antecedent clause of the conditional statement is true and the consequent clause is false.  Theories are routinely falsified as a part of the progress of science.  The paradigmatic case for Popper is the transition from Newton’s mechanics to Einstein’s relativity theory.  Einstein’s theory does not include Newton’s as a special case, but rather contradicts and corrects Newton’s theory, and therefore describes an alternative ontology.  And in such cases the new theory offers a higher degree of information content as indicated by the relative sizes of the classes of potential falsifiers, such that even before empirical tests are attempted it is possible to recognize that the new theory is preferable if it survives the test.

Crucial experiments are methodologically and historically important decision procedures in the progress of science.  In the case of the transition from Newton’s theory to Einstein’s theory a crucial experiment was performed in 1919, in which Einstein’s theory made the more accurate prediction within the range in which the deviation between the two theories was experimentally distinguishable.  Crucial experiments are not only effective for deciding between theories, but are characteristic of the growth of science toward greater information content and verisimili­tude.  Popper rejects the wholistic variation on the arti­factual theory of meaning, because it implies that crucial experiments are invalid, since the alternative theories cannot share common background assumptions with univocal semantics, and since it implies in general that scientific criticism is undecidable.  Both in his 1982 introduction to Realism and the Aim of Science and as early as his 1934 Logic of Scientific Discovery Popper maintained that the falsifying basic statements like all empirical statements cannot be verified, and that therefore it is impossible to prove conclusively that an empirical scientific theory is false.  He also states that every falsification can be retested to motivate an agreement among interested scientists about the test outcome. 

Popper maintains that there have historically been successful scientific revolutions, which were occasioned by successful falsifications, and he rejects the view that falsification plays no rôle in the history of science.  But he offers no theory of meaning description that would enable him to reconcile the phenomenon of semantical change with his thesis of crucial experiments and the rational growth of science.  Contrary to Kuhn, Popper maintains that communication problems are merely difficulties and not impossibilities.  But without a metatheory of semantical description for analyzing semantical change, Popper cannot explain why communication is not impossible, because he cannot explain why it is merely difficult.

Scientific Explanation

Popper’s theory of scientific explanation has been called the hypothetico-deductive thesis.  It is not altogether unique to Popper.  In his chapter on theo­ries in Logic of Scientific Discovery he states that to give a causal explanation of an event means to deduce a statement that describes the event, using as premises of the deduction one or more universal laws together with certain singular statements called initial conditions.  Later in “Aim of Sci­ence” in Ratio (1957), reprinted both in Objective Knowledge and in Realism and the Aim of Science, he defines a causal explanation as a set of statements by which one describes a state of affairs to be explained, statements which he calls the “explicandum”, by deduction from a set of explana­tory statements, which he calls the “explicans”.  The logic of explanation is the modus ponens form of argument, in which a true antecedent clause describing initial conditions and an empirically valid tested and nonfalsified conditional law or theory implies an explicandum consequent clause.  The expli­cans must logically entail the explicandum, and it must not be known to be false.  Furthermore, the explicans must be independently testable, so that it is not ad hoc.

The logical positivist concept of explanation is also described as hypothetico-deductive in the above sense.  But there are fundamental differences between Popper’s and the logical positivists’ views.  Of central importance to Popper’s concept of scientific explanation is the thesis that causal explanation need not describe certain things, or in other words that it need not have a certain semantics describing a certain ontology needed to supply science with foundations, such as the phenomenolist ontology.  Or as Popper says, “science is subjectless”.   Popper’s view therefore differs from the positivist view that causal explanation must have a semantics with such ontological categories as sensations, elementary phenomena, or sense data.  And it also differs from the romantic view of causal explanation in social science, which requires a mentalistic ontology.  In Poverty of Historicism Popper rejects the romantic requirement of intuitive understanding of purpose and meaning produced by sympathetic imagination.  In its verstehen version this mentalistic ontological requirement for causal explanation in social science becomes a theory of scientific criticism.  He maintains that this requirement goes beyond causal explana­tion, and he proposes his doctrine of the unity of method in both natural and social science, the method that he des­cribes in Logic of Scientific Discovery.  In Popper’s philosophy of science “causal explanation” is defined in terms of the function that theories perform in realizing the aim of science, and not in terms of some foundational ontology. 

His view of causal explanation is the result of his rejection of the naturalistic philosophy of meaning.  Without the naturalistic theory of semantics there is no basis for requiring any particular ontology including the particular ontology’s concept of causality, in order to be able to give a causal explanation.  Rejection of the natur­alistic thesis implies the rejection of all ontological criteria for causal explanation as well as the rejection of the semantical distinction between observation language and theory language and of the idea of the existence of an ontological foundation for science.  Thus Popper says that explanation is of the known by the unknown in the sense of conjectural, instead of by the known in the sense of the permanently established foundation.  In this respect Popper is in the company of the contemporary pragmatists; Quine for example calls the view that there are ontological criteria for causal explanation the “genetic fallacy.”

Popper’s rejection of ontological criteria for causal explanation became compli­cated in later years by his idea of metaphysical research programmes.  The metaphysical research programme is not atemporal and eternal like the ontological foundations demanded by essentialists or by the positivists.  It is part of the historical problem situation at a particular juncture in the history of a science, and it is also untestable at the point in time, and therefore “metaphysical” in Popper’s residual sense.  Most notably in Popper’s view, at the given point in the history of the science the metaphysical research program functions as an ontological criterion for what constitutes a satisfactory explanation. 

This complication arises from Popper’s way of demarcating between science and metaphysics, which appeared many years before he introduced the idea of metaphysical research programmes into his philosophy of science, as he did in his later discussions of quantum theory.  As early as 1955 in “Demarcation Between Science and Meta­physics” in Conjectures and Refutations he states that all physical theories say much more than the physicist can test, and that whether this “more” belongs to physics or should be eliminated as a metaphysical element is not easy to say.  And in 1958 in “On the Status of Science and of Metaphysics” reprinted in the same book he says that one can discuss irrefutable metaphysical theories rationally in the sense that one can discuss their ability to solve the problems that they purport to solve, that is, in relation to their problem situation. 

This complication has its origin in the residual status of metaphysics in Popper’s philosophy.  Metaphysics for him contains a great heterogeneity of types of knowledge, which need have nothing in common, but their irrefutable character and therefore their nonscientific status.  Historically philosophers have not treated metaphysics in so residual a manner, but instead have offered positive characterizations of metaphysics, which have sometimes been called “transcendental metaphysics”, and which are not typically viewed merely as protoscience.  For example futile arguments such as realism versus idealism are viewed as transcendental and as incap­able of empirical resolution at any time.  In the concluding paragraph of the concluding section of the concluding volume of the Postscript, Popper states that there may be a criter­ion of demarcation within metaphysics between what he calls “rationally worthless” metaphysical systems on the one hand, and metaphysical systems that are worthy of discussion on the other hand.

He does not characterize the basis for such a demarcation within metaphysics, but his motivation for recognizing the existence of protoscientific metaphysics within residual metaphysics clearly shows the influence of Kuhn.  In the 1982 “Introductory Comments” in Quantum Theory and the Schism in Physics Popper compares metaphysical research programmes to Kuhn’s concept of paradigm, while stressing that metaphysical research programmes must be seen in terms of a situation that can be rationally reconsidered, and that scientific revolutions viewed as changes of paradigms are due to rational criticism.  In this context he references his 1975 “Rationality of Scientific Revolutions”, where he distinguishes between scientific and ideological revolutions, and then sets forth his criteria for rational criticism of scien­tific revolutions like Einstein’s that are applicable even before any experimental testing is attempted.

Aim of Science

Popper’s concept of scientific explanation and the rejection of the naturalistic theory of meaning implied by the falsificationist thesis of scientific criticism, in turn imply a new concept of the aim of science, which is very different from the views of the positivists.  In his philo­sophical development two different types of statements of the aim of science may be distinguished, firstly the logical statement and secondly the later institutional statement.  As early as 1934 in his discussion of the degrees of testabil­ity in the Logic of Scientific Discovery he states that theoretical science aims to obtain theories that are easily falsifiable in the sense that the theories have a large class of potential falsifiers and thus a large information content.  This con­cept of the aim of science is integral to Popper’s view of the growth of scientific knowledge.  Similarly in “Truth, Rational­ity, and the Growth of Knowledge” he states that the task of science is to search for interesting truth in the sense of truth that has a high degree of explanatory power, i.e., empirical information content.  In his later statements Popper added to these ideas of the aim of science the rôle of the historical problem situation with his idea of the metaphysi­cal research programme. 

In the introductory chapter to Realism and the Aim of Science he describes science as a social institution that results from human actions that are unforeseen and unintended.  He states that science grows through the institutionalized cooperation and competition of scientists, who are not only motivated by their own subjec­tive curiosity but also by their motivation to make a contribution to the growth of objective knowledge.  The phrases “social” and “unforeseen and unintended” seem to refer to Popper’s views on the nature of social science and to his rejection of all historical relativism.  Popper defines social science as the study of the unintended consequences of social behavior.  And what are unforeseen in the growth of science are the new theories that result from conjectural scientific research.  The content of theories in future sci­ence is in principle unpredictable in Popper’s view, and he rejects all historicisms that purport to predict history including the history of science.

The strategic relevance of Popper’s reference to the institutional character of science in the context of objec­tive knowledge becomes evident when contrasted with Kuhn’s view that in the history of science the ontology of a pre­vailing theory assumes institutional status.  It seems likely that Popper was led to think of the aim of sci­ence in institutional terms in reaction to Kuhn’s views.  Kuhn’s thesis that the prevailing theory or paradigm assumes institutional status means that the ontology of the prevailing paradigm functions as the criterion for scientific criticism, and that therefore commonly recognized revolu­tionary developments in the history of science, which intro­duce a new theory and ontology into a science, must be viewed as institutional changes with no larger framework providing continuity. 

In Popper’s view this radical discon­tinuity is historical-relativist and irrational.  In his “Rationality of Scientific Revolutions” he quotes Trotsky, saying that the growth of science is “revolution in perma­nence”, but Popper intends this phrase to mean that there exists criteria for scientific criticism that are invariant through even the most revolutionary developments that make scientific change rational and meaningfully progressive.  Thus the force of Popper’s statement that the growth of objective scientific knowledge is a social institution is that the objective nature of science makes revolutionary scientific change occur within an enduring set of insti­tutional value standards, instead of a breakdown of the institution.  The criteria for scientific criticism that operate as the institutional values of the scientific community are in Popper’s view independent of the semantics and ontology of the prevailing theory or paradigm.  As he says in “Normal Science and Its Dangers” in Criticism and the Growth of Knowledge, science is “subjectless”.  In his 1982 “Introductory Comments” to Quantum Theory and the Schism in Physics Popper compares his idea of metaphysical research programmes to Kuhn’s idea of paradigms, but nevertheless maintains that metaphysical research programmes can be rationally reconstructed and rationally criticized, even though they cannot yet be empirically tested.

Scientific Discovery

Popper’s rejection of the naturalistic theory of meaning had the unfortunate consequence of leading him to exclude consideration of the topic of scientific disco­very from philosophy of science.  He viewed philosophy of science as entirely a matter of logic and objective knowledge, while he believes that the topic of scientific discovery is exclu­sively a psychological and therefore subjective matter.  The conjec­tures resulting from the discovery process belong to world 3, but the discovery process itself belongs to world 2, and events in world 2 cannot determine the contents of world 3.  While this view offers very adequate recognition to the freedom in the creative discovery process, it also relegates a whole area of interest for philosophers to the empirical studies of the psychologists.  And as it happens, the topic of discovery has become a central concern of the emerging specialty of cognitive psychology, although Popper would reject the cognitive psychologists’ explicit psychologism. 

Popper’s exclusion of discovery is perhaps due also to his identification of traditional discussions of discovery with the “logic” of induction.  When he rejects inductive logic, he therefore rejects all logic from the discovery process.  He later modified this view, when he explained what he would admit to be possible with an “induction machine.”  Considering the work done by contemporary information scientists working in what is generically called “artificial intelligence” Popper’s later statements are more plausible.  Up to the present time at least, these information scientists would find it difficult to deny that the discovery system user must firstly conceptualize the input to the system.  The discovery systems are not unconditioned much less historicist, and must draw from the current discourse of the science under investigation to develop state descriptions containing their input language.  Thus an alternative to psychologistic analysis is linguistic analysis, which has been characteristic of twentieth-century philosophy.  And linguistic analysis using mechanized generative grammars enables discovery.

Comment and Conclusion

Popper’s philosophy was occasioned by Einstein’s development of relativity theory, a milestone episode in the his­tory of science that Popper took to be paradigmatic of scientific progress.  And Popper’s philosophy is also a mile­stone in the history of philosophy, because it represents a fundamental problem shift.  While Carnap and other positiv­ists continued their efforts to establish theoretical sci­ence including Einstein’s theory, on firm semantical and ontological foun­dations, Popper rejected the naturalistic theory of meaning that supposedly supplies such a foundation, and accepted the revision of scientific explanation as a matter of course.  Positivist foundational problems, such as the problem of the meaningfulness of theoretical terms, became pseudo problems or what Heisenberg called “false questions” as a result of Popper’s problem shift, while the problem addressed by Popper, the rational growth of science without foun­dations, has become central to philosophy of science. 

Popper’s philosophy was not occasioned by the development of the modern quantum theory, and he spent much of his professional career attempting to reconcile his philosophy and the modern quantum theory.  It may be said that just as Carnap had attempted to reconcile positivism and Einstein’s relativity theory, Popper had attempted to reconcile his philosophy and the new quantum theory, except that Popper also presumed to revise the semantical interpretation of quantum theory.  In the meanwhile the pragmatist philosophers have taken up a rôle relative to quantum physics, accepting it as the para­digm of modern physics, that Popper had taken up relative to Einstein’s relativity theory.  As a result Popper’s philosophy now represents the conservative position in the con­temporary professional literature of philosophy, a position that casts him in the rôle of more the defensive rearguard than the aggressive vanguard he had been.

One of the distinctive aspects of the historical development of quantum theory is the persistent plurality of semantical and ontological interpretations compatible with both the same experimental measurements and mathematical formal­ism.  This plurality has caused lengthy controversies among the physicists; Landé’s list of seven alternative interpre­tations may be taken as indicative of this plurality.  Pop­per’s response to this situation in modern microphysics was to create still another interpretation for the quantum theory, his particle-propensity interpretation, because like Einstein he rejects the schism in physics and believes that a uniform ontology for both microphysics and macrophysics is imperative. 

The history of physics has since evolved differently than Popper had imagined. Since the 1990’s there has been a successful replacement of the traditional language with its classical concepts by a new lang­uage, which is better adapted to the mathematics of quantum theory.  In his Understanding Quantum Mechanics Princeton University physicist Roland Omnès reports that recent conceptual developments using the Hilbertian framework have enabled all the features of classical physics to be derived directly from Copenhagen quantum physics.  And he says that this mathematics of quantum mechanics is a “universal language of interpretation” for both microphysical and macrophysical description.  This deductive relationship has not only resolved Heisenberg’s “everyday” language, but because it is deductive, it has even further resolved the vagueness in the semantics of the vocabulary in both macrophysics and microphysics.

The pragmatists reacted differently than Popper.  For them the quantum theory is the paradigmatic episode in the history of science, and their more accepting attitude has occasioned another problem shift in philosophy of science.  While some pragma­tists express reason to advocate one or another particular interpretation of quantum theory as distinctively interest­ing from the viewpoint of philosophy of science, the reason is not the particular philosopher’s prior ontological commit­ments.  Rather it often proceeds from a belief in the importance of the particular interpretation for scientific discovery.  As Hanson noted at the opening of his Patterns of Scientific Discovery, the issue for physics affects the strategies for future research.  (Dis­covery, remember, is the topic that Popper did not consider even being a part of philosophy of science).  The focus on the problem of scientific discovery has in turn occasioned the problem shift: philosophers have reconsidered the semantical and ontological pluralism represented by the different interpretations of quantum theory.  They have concluded that the pluralism is an inevitable outcome of the empirical underdetermination of language, and that it is therefore a strategic condition for continu­ing the growth of science.  (Growth is the topic that Popper considered being central to philosophy of science).  In brief – Popper’s approach is to attempt to adjust the seman­tics and ontology of quantum physics to his philosophy of science, while the pragmatists’ approach has been to attempt to adjust philosophy of science to account for the phenomenon of semantical and ontological pluralism in science and to identify its function.

As it happens, Popper’s rejection of the naturalistic theory of meaning supplied the pragmatist philosophers with the point of departure for addressing this phenomenon of semantical pluralism, and they did so in ways that Popper did not accept.  The philosophical view that affirms an artifactual character of the relativized semantics of language admits to a wholistic variation that introduces an unresolvable cultural and historical relativism into science, which in turn makes problematic the intersubjective objectivity and rationality that Popper considers to be necessary for the growth of science.  Popper recognized the philosophical views of the historian of science, Thomas Kuhn, as paradigmatic of this semantical wholism.  The affirmation of this wholistic variation and its consequent ambiguity is occasioned by the thesis that scientific change involves semantical change.  Popper’s philosophy does not address the problem of semanti­cal change, because he identifies all attempts at semantical description or “meaning analysis” with disreputable essentialism.  As a result contemporary philosophers of science have moved on to new problems that Popper was unprepared and unwilling to address. More importantly neither Popper nor pragmatists such as Hanson, Kuhn or Feyerabend had any concept of componential semantics as an alternative to wholism.

Finally some comments are in order about Popper and the positivists’ truth-functional logic. In addition to criticizing the logical positivists for their positivism, Popper also refrained from using their favorite logic, the Russellian symbolic logic.  This logic is called a truth-functional logic, because the truth value of any compound statement, such as a conditional “material implication”, can be determined by reference to the truth-values of its component elementary statements.  Therefore in the truth-functional logic the truth tables for all compound statements are complete for all combinations of truth-values of the component statements, thus enabling the symbolic logic to have the closure of an algebra, which is very desirable for a mathematical system including mathematical logic. Originally the agenda of the symbolic logicians was to make logic the foundation for mathematics.  Ironically these Russellians had firstly to make logic into mathematics before they could make their symbolic logic a foundation of mathematics.  In contrast the nontruth-functional conditional statement affirms the existence of a dependency connection between the truth-values of the antecedent and consequent clauses, such that the truth of the conditional compound statement is not determined merely by the truth-values of the component clauses for combinations of truth-values. 

The affirmed dependency connection might for example be a logical one, as obtains between the premises and conclusion of the categorical syllogism.  The conditional statement expressing a syllogism would have an antecedent clause consisting of the conjunction of the major and minor premises and a consequent consisting of the conclusion.  As is well known, the conditional connection is the logical inference, which may be valid independently of the truth of its constituent statements – either in the conjunction of the premises in the antecedent clause or in the conclusion in the consequent clause.  The logical inference may be invalid such that the conditional statement is false, while both of the premises in the antecedent and the conclusion are be true. Thus the conditional statement’s connection is not truth-functional.

But of greater interest in philosophy of science are those cases in which the nontruth-functional connection is an empirical hypothesis affirming a causal connection instead of a logical connection.  In the modus tollens form of argument, if the antecedent clause describing the initial conditions of a test is false, then the truth of the conditional statement expressing the tested theory is irrelevant or unknown, because the empirical test is not valid when it is not executed in accordance with its test design described in the antecedent clause.  But if the antecedent is true, the test is valid, and if the test outcome is not a falsification, then the theory can reasonably be believed to be true for the time being, but its truth is not logically established.  The truth condition of the nontruth-functional conditional statement is logically implied from the truth of its component statements only in the event of falsification.

Consider the stereotypic universal “Every raven is black”, which Popper would consider a theory, since the statement is universal and because he considers all descriptive terms to be a type of theoretical term which the positivists called “disposition terms.”  Then re-express the universal categorical proposition as a conditional statement in the form of a material implication of the Russellian predicate calculus:

This is conventionally rendered in English as “For all x, if x is a raven, then x is black”, or more colloquially as “For every entity, if the entity is a raven, then it is black.”  Popper’s falsificationist thesis of scientific criticism requires a nontruth-functional logic in which only the falsehood of the universally quantified conditional can be determined from knowledge of the truth values of its component elementary statements.  In this case the conditional is a hypothesis or theory proposed for empirical testing. 

Thus the truth tables for truth-functional conditional and the corresponding nontruth-functional conditional logical forms are different.  The Frege-Russellian “logistic” agenda to reduce mathematics to logic motivated the symbolic logicians to construct the truth-functional logic that is a closed mathematical algebra.  Thus the irony noted above: the “logisticians” who wanted to make logic a foundation for mathematics firstly had to make their logic a branch of mathematics.   The result misled many philosophers of science.  The logical positivist philosophers had deluded themselves into thinking that they are very sophisticated and impressively technical by using the Russellian mathematical logic, and they exercised themselves with their favorite problem of the significance of so-called theoretical terms.  The truth-functional truth table dictates that the truth of the antecedent and consequent atomic sentences can logically conclude to the truth of the material implication conditional expressing an empirical universal statement.

Yet these philosophical descendents from Hume eventually recognized that their Russellian conditionals are not eternal verities like their observation sentences.  Nonetheless for decades the symbolic logic ostentatiously littered the pages of the Philosophy of Science and British Journal of Philosophy of Science journals with its chicken tracks, and rendered their ostensibly “technical” papers fit for the bottom of a birdcage.  Finally even the lesser lights among the positivists came to recognize that the technical pretenses of the Russellian logic could not supply the façade of sophistication that had formerly masked its sophistic claim to be the logic for science, and the Russellian symbolic logic has largely fallen into disuse. Good riddance to bad rubbish!


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