Before Popper, Kant had proposed a solution to Hume’s problem that also called for knowledge that relates to the world of observations while preceding those observations. The difference is that, for Kant, this knowledge is a priori truths, which puts this attempt at a solution in the first horn of Hume’s fork, whereas for Popper this knowledge is fallible conjecture—he does not try to circumvent Hume’s argument. On the other hand, they have in common that this knowledge is intersubjective. Intersubjectivity suggests in Kant the existence of an objective or “external” reality, i.e., common to all subjects. the importance of “agreement of judgments”. For Zahar, in Popper’s philosophy, “intersubjectivity and objectivity are synonymous” and Stokes makes the same point. However, still according to Boyer, for Popper one cannot know if the objective knowledge of science is true. Boyer explains that, according to Popper, Kant was misled by his erroneous belief in the truth of Newtonian physics, so true for Kant, Boyer will say, that it is a priori. Moreover, for Kant , Newton did not need creativity to find his theory: it could be deduced systematically from accessible a priori knowledge—it was itself in this way a priori knowledge. Popper rejects this. Dwayne Mulder, in his article on objectivity in the Internet Encyclopedia of Philosophy, notes that it is important to distinguish between two kinds of objectivity: one applies to knowledge or judgment and the other to reality itself. For Kant, science will never reach the knowledge of things in themselves. Popper accepted truth as the guiding idea and in this he approached Kant’s a priori truth, without however accepting that a scientific theory could be known to be true. For Popper, scientific objective knowledge consists of conjectural theoretical models with an empirical interpretation allowing a confrontation with observation.
Object language, metalanguage and state of affairs
At the beginning of the 20th century, to avoid inconsistencies, logicians distinguished between object language and metalanguage. This distinction is similar to that between formal equations and the situational problem in a simple process of equating: as with formal equations, object language expresses only certain relations and ignores other aspects. In this purely pedagogical analogy, the laws or axioms stated in the object language are like equations used to solve a situational problem. Popper will insist that falsifiability exists at the level of the language of theory which abstracts from the methodological problems of refutation, i.e., at the level of logic. Insofar as this language has an empirical interpretation, an observation described in this language is an imaginable state of affairs, but this state of affairs may not correspond to any fact and therefore be imaginary.
Intersubjectivity and the criterion of truth
Popper also sees in this separation of language and metalanguage, more specifically in Tarski’s theory of truth, support for the notion of objective truth, but Tarski responds that his theory is “epistemo-logically neutral”. In this regard, Chalmers turns against Popper the need to distinguish between theory and methodological reality in which theoretical laws are no longer isolated. Chalmers accepts factual correspondence in the case of “everyday speech” statements such as “snow is white” given by Popper as an example, but raises the methodological problems that arise when trying to apply this correspondence more generally in science. Zahar has a similar critique: if objectivity and intersubjectivity are synonymous, objective truth cannot be correspondence with facts, because “external reality is beyond reach, it is transcendent” while the sentences, as linguistic entities, are not a problem since we create them ourselves; so we have access to it. Linguistic entities are objective. In addition to these criticisms, Popper self-criticizes his use of intersubjectivity: Robinson Crusoe could develop and test science on his island. Already in 1930-1933, he admits that the control pursued by a single individual already has something akin to intersubjective control. (The sociological character is therefore not — at least in many cases — of decisive importance.) However, for Popper, the scientific method involves collective control. Scientific objectivity, according to Popper, is not the business of the researcher alone, but necessarily requires the critical cooperation of other researchers. It is based on an intersubjective method. On this point, Otto Neurath mentions that the success of Robinson Crusoe requires the intersubjective properties of language. Moreover, according to Popper, the methods available to Robinson Crusoe do not guarantee the elimination of certain errors which can be eliminated by its methods. If for Popper truth is an informal correspondence with facts, this correspondence must be judged by a sociological phenomenon. On this last point, he joins other philosophers before him such as George Herbert Mead.
(Includes texts from Wikipedia translated and adapted by Nicolae Sfetcu)