Since the 1920s, when Karl Popper proclaimed his principle of falsification as the basis for the testability of knowledge and for distinguishing between scientific propositions and pseudo-science, he has invariably criticised positivist philosophy and its understanding of objectivity as the observability of events. His arguments against empiricism are serious enough. Popper maintains, first, that observation is always based on some theoretical premises and that scientific knowledge, contrary to the positivists, does not start with sensory data. Hence, the objectivity of knowledge cannot be identified with the observability of events. Second, the traditional problem of inductive conclusion regarded by empiricism as the principal argument in favour of the objectivity of a theory is rooted in Hume’s error regarding the nature of the scientific method.

However, the true significance of this criticism can only be assessed in the light of Popper’s positive programme. It may appear at first sight that the principles of his epistemology are indeed radically different from those of positivism. Knowledge, according to Popper, cannot start from nothing—from a tabula rasa—not yet from observation. Science, philosophy, rational thought, must all start from common sense. [1]

Yet the main principle of common sense is the faith in the existence of the real world. Realism which asserts the existence of the world outside and independent of its perception cannot, in Popper’s opinion, be proved or disproved. In other words, it belongs to the sphere of “metaphysics”. Realism should be accepted “as the only sensible hypothesis—as a conjecture to which no sensible alternative has ever been offered”. [2] Popper’s realism, however, has little in common with “scientific realism” or “scientific materialism”, particularly in the understanding of objectivity. In Popper’s opinion, shared also by enlightened common sense, “realism should be at least tentatively pluralistic.” [3] A rationalist seeks to reduce all the diversity of the world to several fundamental entities or processes. In Popper’s words, Ockham’s razor can only be applied after recognising the plurality of what there is in the world. [4]

As has been indicated earlier, Popper distinguishes three autonomous and relatively independent worlds noting that the term “world” is conventional and that there may be different criteria for their classification. The “first world” is physical reality, the “second world” the subjective knowledge of an individual, and the “third world”, objective knowledge as understood by Popper. “My first thesis,” Popper writes, “involves the existence of two different senses of knowledge or of thought: (1) knowledge or thought in the subjective sense, consisting of a state of consciousness or a disposition to behave or to react, and (2) knowledge or thought in an objective sense, consisting of problems, theories, and arguments as such. Knowledge in this objective sense is totally independent of anybody’s claim to know; it is also independent of anybody’s belief, or disposition to assent; or to assert, or to act. Knowledge in the objective sense is knowledge without a knower: it is knowledge without a knowing subject.” [5] The elements of the “third world” comprise, according to Popper, not only theories and ideas, but also problems or problem situations. By analogy with physical states he also qualifies as the “third world’s” elements the states of discussion or the states of critical arguments, as well as information carriers, i.e. books, magazines, libraries, etc.

It is indicative in itself that Popper’s evolution has brought him to the recognition of the existence of the “physical world”. Yet the sequence of the worlds as listed above by Popper does not correspond to their significance in Popper’s logic of science. It is not at all the physical world occupying the first place on Popper’s list that constitutes the essence of scientific knowledge. Nor is the “second world”, i.e. the world of emotions, sensations and individual knowledge, of any great significance. In Popper’s opinion, it is just because of its exclusive interest in the subjective knowledge as expressed in everyday phrases “I know” or “I am thinking” that traditional epistemology has lost its influence. It was concerned with what was not, in fact, scientific knowledge. Popper writes: “For scientific knowledge simply is not knowledge in the sense of the ordinary usage of the words ’I know’. While knowledge in the sense of ’I know’ belongs to what I call the ’second world’, the world of subjects, scientific knowledge belongs to the third world, to the world of objective theories, objective problems, and objective arguments.” [6] Hence, the “third world” or “world 3” alone is truly autonomous and objective.

From the epistemological viewpoint this thesis does not offer any new solutions. It only counters empiricism in that it eliminates the question of the source of knowledge, as the logic of scientific discovery which is the core of Popper’s entire epistemology has no place for such question. It lies on the other side of the “line of demarcation” drawn by Popper between science and metaphysics. Yet even within the narrow limits of the logico-theoretical model of knowledge the concept of the “third world” gives rise to serious contradictions. If we analyse the relation of the “third world” to a concrete discovery or theory, we are bound to answer at least two questions: first, which element of our knowledge and at what stage of its maturity is regarded as the initial one? Second, which elements in a given discovery or theory can be confirmed or disproved by an experiment? Popper gives in fact no answer to the second question. As regards the first one, the answer is as follows: the selection of the initial, basic propositions is a conventional one. Popper does not deny the connection of basic propositions with experience. In The Logic of Scientific Discovery he writes that a decision to adopt a basic proposition is not prompted by our sense-perceptions. According to Popper, experience can only motivate a decision to adopt a proposition or reject it, but any attempt to trace basic propositions to perceptions will prove completely futile.

Hence, despite Popper’s resolute opposition to empiricism, his concept reveals curious likeness to logical positivism in at least two respects. First, Popper strives to confine the subjectmatter of epistemology to purely logical problems and to dismiss some problems of general significance (e.g. the problem of the source of knowledge). Second, like the representatives of the Vienna school Popper is forced to resort to conventionalism as regards the origin of basic propositions. In point of fact, he replaces the conventionalism “from above” (in relation to laws and theories) characteristic of logical positivism by conventionalism “from below” (in relation to basic propositions). His conventionalism stems from deeply rooted logicism which manifested itself already in his early works by the rejection of philosophical and sociological problems of science. Understandably, Popper’s basic propositions do not relate to current individual experience, but reflect the system of established knowledge. His concept has not gone beyond a slight displacement of the border between our knowledge and the material world. All we know from Popper about our relation to this world is that our knowledge exerts active influence upon it. He sidesteps the question of the primacy in this interaction which is embarrassing to both the positivist and Popperian epistemology and constitutes the key issue of the theory of knowledge.

According to Popper, the “third world” emerged as a result of the spontaneous activity of man and this is just what accounts for its objectivity. The unpremeditated build-up of knowledge by man is akin to the spinning of a web by a spider or to the making of honey by a bee. “And I assert,” writes Popper, “that even though this third world is a human product, there are many theories in themselves and arguments in themselves and problem situations in themselves which have never been produced or understood and may never be produced or understood by men.” [7] Such theories and problem situations, according to Popper, do not appear according to plan, they are not even needed before their emergence. Once they have made their appearance, however, they may create new problems or a new system of ideas. The objectivity of a theory is understood by Popper as its independence from individual consciousness. In order to substantiate his viewpoint, he concentrates, first and foremost, on the problem of the acceptance and understanding of scientific discoveries.

It should be noted that this problem is not alien to Marxist philosophy either. It has long since been the object of serious discussions in Soviet literature relative to concrete dialectical issues. The true meaning of ideas, theories and projects is indeed often realised by scientists long after the corresponding discovery or invention is made. This fact, characteristic of one of the aspects of objectivity, is not regarded by Popper as something requiring any special attention. Actually, however, the gradual realisation and acceptance of a discovery is nothing but the result of the objectivity of knowledge understood as the reflection of objective processes, i.e. as a fact which can only be explained through the analysis of social factors influencing the development of science and its relation to the material world.

Ideas, theories and other components of social consciousness are indeed relatively autonomous and independent of individual consciousness. The existence of the theory of relativity or Darwin’s theory of evolution does not depend on anyone’s consciousness. Moreover, we can go even so far as to assert that it was not Einstein or Darwin who had to decide on whether their theories were “to be or not to be”. These theories were bound to appear, and not at the scientists’ wish or by force of coincidence, but mainly because they reflected the objective processes of reality. Besides, to understand the inevitability of these discoveries, one ought to take into account the general laws of scientific development determined in the end by practical needs. Hence, the correct statement of the problem of objectivity is the following: what is the objective content of scientific theories and what are their subjective elements?

Frankly speaking, Popper’s analysis of a scientific theory cannot boast of subtlety. Knowledge is construed as both a process of cognition and a result thereof, embodied in various theories, ideas and problems. In Popper’s opinion, however, the process of thinking lies outside the concept of scientific knowledge which should be mainly understood as the product of this process, i.e. as theories and their logical relations. The process of thinking is always individual and subjective, whereas its general results, i.e. problems, ideas and theories are objective. In Popper’s opinion, the incompatibility of certain theories is a logical fact which is absolutely irrelevant to whether somebody is aware of it or not. These purely objective logical relations are the characteristic features of entities which are called by Popper theories or knowledge in the objective sense of the word.

Should we defy Popper’s scheme, overstep the boundary set by him and consider the connection between scientific knowledge (the “third world”) and material reality in all details, i.e. in the process, sum, tendency, origin, we shall find out that there is no sharp line of demarcation between the knowledge of an individual and the system of scientific knowledge developed by mankind. They differ, as it were, by the objective/subjective ratios. Hence, both the thinking processes and their results deserve special philosophical analysis. The electromagnetic theory as developed by James Maxwell was evidently just as much indicative of its author’s subjective demerits (and, for that matter, his subjective merits), as were his mental processes, notions and ideas. To be sure, science cannot be too tolerant. The amendments made by Heinrich Hertz and Oliver Heaviside, as well as the subsequent elaboration of the electromagnetic theory in the light of the theory of relativity and quantum mechanics have corrected a number of Maxwell’s errors. Yet it is not criticism or mutual rational verification which guarantees, according to Popper, the objectivity of the electromagnetic theory. Such criticism can at best eliminate some subjective imperfections thereby helping to reveal the objective content of the theory. It does not mean at all that a scientific theory owes its objectivity exclusively to criticism and falsification of erroneous conclusions.

Despite the proclaimed objectivity of the “third world”, Popper fails to provide an appropriate substantiation for this thesis. His objectivity can only be defined by comparison with individual experience, and the criterion of the testability of theories is, in fact, intersubjective by nature. Popper himself makes no bones about his stand when he writes: “Now I hold that scientific theories are never fully justifiable or verifiable, but that they are nevertheless testable. I shall therefore say that the objectivity of scientific statements lies in the fact that they can be inter subjectively tested.” [8] Intersubjective testing need not go beyond a mutual rational control which is the common objective of critical discussions. Such rational control, according to Popper, ’is only possible through multiple checks and repeated comparisons with the obvious. No observations should be taken into account if they cannot be repeated and checked. Such repetitions alone can provide sufficient evidence that we deal not with accidental coincidences, but with events which are intersubjectively testable owing to their recurrence. In other words the objective world as defined in Popper’s epistemological scheme is mainly referred to by scientists for falsification of one or another theory.

According to Popper, the essence of scientific activity, its distinguishing feature consists in systematic attempts to refute ideas, hypotheses and theories which are being advanced, and in eliminating errors. The tests should result in the selection of a hypothesis which is more resistant to criticism than other hypotheses. In other words, all tests should aim at finding weak points and eliminating untenable theories by their falsification. “But just because it is our aim to establish theories as well as we can,” writes Popper, “we must test them as severely as we can... This is the reason why the discovery of instances which confirm a theory means very little if we have not tried, and failed, to discover refutations.” [9] Yet Popper overlooks the fact that every experiment tests not only a theory as such, but also a host of its logical and non-logical premises. All of them participate in the interpretation of an experiment in one way or another. Therefore, if an experiment testifies against a theory, we can never be sure whether the falsification applies to the theory itself, or to the attending premises. The conclusion that an experiment falsifies a theory is purely conventional. Any theory can be saved by introducing additional premises or by modifying the basic ones. Realising the contradictory nature of the situation, Popper offers, on purely conventional grounds, to adopt a postulate prohibiting the introduction of hypotheses intended to protect a theory against a “death sentence”.

Consequently, in Popper’s opinion, theories and ideas must become the objects of merciless falsification. The refutation of theories becomes for scientific cognition the end in itself.

In accordance with his model of scientific cognition Popper contends that not a single scientist can claim the truth of his ideas and theories. “Scientists act,” he writes, “on the basis of a guess or, if you like, of a subjective belief (for we may so call the subjective basis of an action) concerning what is promising of impending growth in the third world of objective knowledge.” [10] In developing their research programmes scientists, according to Popper, are guided by their conjectures as regards which trend is likely to be the most fruitful in the “third world”. A scientist therefore must once and for all discard the self-confident “I know” or “I suppose”. Since his individual notions are inevitably subjective, he has but very modest rights which only entitle him to say: “I am trying to understand a problem”, “I am trying to think of alternatives to this problem”, “I am thinking of an experimental check for the given theory”, “I am trying to axiomise the theory”, and the like.

According to Popper, the worlds are real if they can interact with the physical world, and they are autonomous if their irreducibility to one another is postulated. The main problem of his pluralistic philosophy hinges upon the relations between the worlds. Of the three worlds, the two first and the two last ones can directly interact. The second world, the world of individual experience, subjective knowledge, can interact with the two other worlds, but the physical world and the world of knowledge cannot directly contact each other in a similar manner, they have to use the mediation of the second world. In principle, it is possible to assume the reducibility of the mental world to the physical world, but the existence of objective knowledge, its obvious influence on the physical world, on the one hand, and the no less obvious impossibility of the direct causal effect of abstract entities on physical processes, on the other, force the inevitable conclusion about the plurality of the worlds and the autonomy of the mental as the necessary mediator between the physical and the ideal.

One of the important functions of the “second world” is to comprehend the objects of the “third world”, i.e. the objective content of thinking. Almost all subjective knowledge depends on objective knowledge. The “third world” is autonomous, though we constantly act upon it and are subjected to its influence. Cognition is traditionally defined as the activity of a cognising subject. Popper holds that this definition is only applicable to subjective cognition which should better be called organic cognition as it “consists of certain inborn dispositions to act, and of their acquired modifications”. [11]

Objective cognition does not depend on the cognitive aims, opinions and actions of the cognising individual. Cognition in the objective sense is cognition without the cognising individual. Objective knowledge consists of the logical content of scientific theories, conjectures, suppositions and logical content of their genetic code. Objective knowledge can be exemplified by scientific theories expounded in journals and books, discussions of these theories, as well as by problems, problem situations, etc.

From the viewpoint of traditional subjectivist epistemology, the “third world” can only exist as the content of some consciousness. For instance, a book only exists as a factor of culture if somebody reads it. A book remains a book even if it is a table of logarithms composed by a computer and not written by any man. A book belongs to the “third world” provided it can be understood and deciphered—even if such a possibility is never translated into reality. In Popper’s opinion, Plato was the first philosopher who discovered the existence of the “third world”, its influence upon us and began to use the ideas of the “third world” to explain the phenomena of the “first” and “second” worlds.

The history of epistemology knows a far more influential tradition than the one Popper claims to represent. Epistemological subjectivism, like its antagonist, ontological realism, are both rooted in common sense. The everyday concept of knowledge rests on the conviction that sensory data are the source of knowledge. In philosophy this concept is known as the theory of tabula rasa. It underlies Locke’s, Berkeley’s and Hume’s empiricism, as well as many theories of modern positivists and empiricists. Traditional non-critical rationalism contrasting itself to empiricism and subjectivism has also, proved unable to overstep the bounds of common sense.

The subjectivist theory of knowledge is incapable of distinguishing between subjective and objective knowledge. In its attempts to disclose the process of scientific cognition traditional (positivist) epistemology proceeded either from sense data, or from the self-consciousness of a cognising individual “(I know”, “I think”), remaining in both cases within the narrow confines of subjective knowledge. Naturally enough, it could not understand it either, since the comprehension of the “second world” is only possible from the positions of the “third world”.

According to Popper, the theory of knowledge of common sense is almost entirely false, yet its main error consists in the search for a self-evident starting point of the process of cognition. Classical epistemology was incapable of understanding that sensory data were nothing but adaptive reactions of an organism. The organs of sense, such as the eyes, are not indiscriminate in their perception of the surrounding world; they take in only those events which are being “expected”, and no others. Like theories (and prejudices), they must be “indifferent” to other events which they do not perceive and cannot interpret. Any sensuously perceived material, according to Popper, is already an interpretation based on a theory or on prejudice. There can be no “pure” sensory experience, just as there can be no “pure” language of observation: all languages are full of myths and theories.

Rejecting epistemological reductionism, Popper also comes out against ontological reductionism (physicalism). Criticising physicalism as a variety of radical materialism, Popper alleges that the latter is incapable of explaining the qualitative diversity of reality. In his opinion, materialism could have had some sense before the appearance of life on the earth. After that, owing to the development of human culture and self-reflection of man, physicalist explanations lost their universality. As man has created a new objective world, the world of the products of the human mind, a world of myths, of fairy tales and scientific theories, of poetry and art and music, the emergent, creative nature of the universe becomes, in his opinion, quite obvious. [12]

All the three worlds, according to Popper, are real. Speaking of the reality of “world 1”, Popper agrees with the physicalist materialists that notions used by a physicist, such as fields, forces, quanta, etc., refer to real entities. Yet, in his opinion, traditional materialism with its paradigm of reality in the form of solid material bodies is closer to the truth. He shares the viewpoint of common sense that physical entities are just as real as consciousness understood as subjective mental process, as well as the content of consciousness embodied in culture. The central point of Popper’s concept is his assertion of reality and the relative independence of “world 3”, the world of the products of human spirit such as legends, explanatory myths, instruments of knowledge, scientific theories (both true and false), scientific problems, social institutions and works of art.

It is noteworthy that Popper links the existence of the objects of “world 3” with the embodiment of the products of human intellect in books, sculptures, etc. However, the mere “objectification” of these phenomena in material culture and in the systems of signs does not yet testify to their independence. Popper’s crucial argument in favour of the autonomy of “world 3” consists in that the development of theories and ideas follows their own laws and they produce consequences which cannot be foreseen by their creators. Being ideal as they are, they can also give rise to material effects: for instance, they can induce people to produce their own kind and other ideal objects thereby exercising influence on “world 1”. All civilisation, according to Popper, can be regarded as the realisation of man’s aims, ideals and plans, i.e. the objects of “world 3”.

The distinction of Popper’s concept from physicalist theories stands out quite clearly here: he refuses to substitute the epistemological problems of the correlation of the “mentalist” and “physicalist” languages for ontological problems, seeks to deduce the qualitative diversity of the external world from reality and posits the problem of consciousness in the context of cosmic and cultural evolution. On the other hand, Popper reveals no less clearly the inadequacy of his understanding of the interdependence of the subjective and the objective consciousness. The concept of autonomous “world 3” gives grounds for a supposition that the emergence of new ideas is determined by logical possibilities which have already materialised in the objects of this world, i.e. in theories, problem situations, etc. In that case ideas and theories must have ideal existence even before they enter individual consciousness and the task of the subjective spirit must consist in provoking the realisation of ideal possibilities lying dormant in human culture, i.e. in translating possibility into reality. More, if we assume that the activity of the subjective spirit is confined merely to “grasping” and manipulating the objects of “world 3”, we are bound to deny the spontaneous creative activity of human consciousness and to admit that individual consciousness and new ideas are products of culture, but not of concrete individuals. Popper is evidently not completely unaware of this Platonic tendency in his concept and therefore lays special emphasis on the genetic-biological foundation of consciousness and knowledge.

Denouncing the philosophy of neopositivism, particularly its claim to the role of the methodology of modern scientific cognition, Popper in fact offers an idealistic epistemological alternative.

To substantiate his understanding of the progress of scientific cognition, Popper introduces a concept of “verisimilitude”. In his opinion, the verisimilitude of a theory consists in the superiority of a multitude of true logical consequences of this theory over a multitude of false logical consequences. From this viewpoint, of crucial importance is the content of a theory. It includes a class of all logical consequences, both true and false. Popper intends to divide this system, evidently infinite, into two subclasses—the true and the false consequences of the given theory, and to discard successively those which themselves ensue from false consequences.

It should be noted that the very notion of logical consequence is not used by Popper with due accuracy. Individual statements, some of which are based on or expressed in theories, evidently have no consequences at all (true or false). A consequence is only possible in situations where certain initial conditions are indicated. In that case, however, the number of consequences will be equal to the number of statements contained in the description of initial conditions. Most of them will probably turn out to be false in the strictly logical sense of the word, since the accuracy possible under experimental conditions can hardly compare with the accuracy of mathematical operations associated by Popper with the notions of truth and objectivity.

Besides, in a situation with the infinite number of consequences there will be only two degrees of verisimilitude, the maximum and the zero one, depending on whether the true content is infinite and the false content is finite, or both of them are infinite. The vulnerability of Popper’s concept of verisimilitude is noted, for instance, by American philosopher G. S. Robinson, who writes: “If scientists were to take Popper’s conception of verisimilitude and progress seriously it would have the effect of stultifying growth and progress because what he calls ‘verisimilitude’ and ’progress’ could be increased or even maximized by a policy of incurious repetition of safe experiments.” [13]

Contrary to Popper, scientists do distinguish between theories and predictions ensuing from them considering some of them truer than others. For instance, planning a flight to Venus, they are sure that the theory of relativity is more reliable than the theory of Newton, Ptolemy or Aristotle and that the predictions based on the former must be more accurate than those based on the latter. Of course, scientists may err in their judgements of relative probability. Their inductive criterion of truth may sometimes fail them. Yet they do use it and rely on one theory more than upon another. If Popper refuses to admit that we can and must express judgements on comparative probability based on an inductive conclusion, his theory of verisimilitude and progress proves untenable. If the predictions of an old theory (except a small number of tested ones) have turned out false and the predictions of a new theory (except a small number of rejected ones) have turned out true, it is obvious that the new theory is closer to the truth than the old one. It stands to reason that a scientific theory owes its reputation for dependability to a successful experimental or practical test. Why, then, is its rational confirmation not possible? “If any and every failure to fit were ground for theory rejection,” Thomas Kuhn justly observes, “all theories ought to be rejected at all times. On the other hand, if only severe failure to fit justifies theory rejection, then the Popperians will require some criterion of ‘improbability’ or of ‘degree of falsification’. In developing one they will almost certainly encounter the same network of difficulties that has haunted the advocates of the various probabilistic verification theories.” [14]