According to Popper, falsifiability provides a solution to the problem of induction, raised by Hume, and to that of demarcation, which he also calls Kant’s problem. Popper explains that he was influenced by Kant, but benefited from a different context: as much as Newton inspired Kant, so Einstein’s refutation of his theory inspired Popper. For Kant, Newton’s theory was “so true”, Boyer would say, “that it was a priori“. Kant’s philosophy is a synthesis of rationalism and empiricism, seen at the time as the two classical theories of knowledge. In Kant, Newton’s theory supports rationalism. Empiricism is represented by the influence of a noumenal reality. For Kant, observations in science fall between these two extremes: on the one hand, the reason by which we obtain the universal laws which impose themselves in observation and, on the other hand, a noumenal reality which determines what will be observed without ever being directly accessible. Knowing that Newton’s theory has been refuted by Einstein, Popper places it in a world of fallible knowledge whereas Kant, respecting the point of view of his time, places it in a world of laws both infallible and human. According to Kant, says Boyer, it is we who inform reality, who give it its shape: the object settles on us. This a priori world of Kant does not entirely disappear in Popper, but there remains only a world of subjective, even biological knowledge, separated from our objective knowledge, governed by an evolutionary theory and including innate predispositions. In the same way that, in Kant, our observations are the result of a synthesis of an a priori world and a noumenal empirical world, in Popper the subjective world and the empirical world have and must have an influence on our fallible objective knowledge. Popper’s solution to the problem of induction is, he admits, a Kant-inspired synthesis of rationalism and empiricism, but the empirical world has a more prominent role in Popper, as it is used in the approach criticism that Einstein had against Newton’s theory.
Popper defined refutability to align with this critical approach and resolve the problem of the demarcation between scientific knowledge and other forms of knowledge. The question of how to distinguish scientific knowledge from other forms of knowledge has always fascinated philosophers, especially those of the Vienna Circle with whom Popper interacted extensively. A major difficulty was that observation is laden with theories, i.e. one cannot understand observation without a theory to at least partially explain measuring instruments and other theories. to explain the larger context for understanding this theory. Popper is aware that this leads to endless regression. Popper’s solution is to distinguish between a so-called logical level and another so-called methodological level. The logical level is the one in which we formulate a theory such as universal gravitation and the basic statements. A methodological decision must be made to define the logical level and the corresponding basic statements. This does not mean that it is impossible to give the theory explaining the basic statements, but a decision is made to consider this as belonging to empirical interpretation. The existence of this empirical interpretation is the material condition of refutability. This is not a formal requirement, because of infinite regress. Refutability also requires that the theory be contradicted by basic statements.
To respond to Lakatos who suggested that the refutability of Newton’s theory was as difficult to demonstrate as the refutability of Freud’s theory, Popper gave the example of an apple that rises from the ground to a branch and then turns to dance from one branch to another. This is clearly impossible, but it is a basic statement, because the position of the apple at different times can be measured, and it logically contradicts the theory. Methodologically, this is just a “potential contradiction”.
Long before Popper gave it its meaning as a boundary criterion, falsification in the usual sense of “subject to falsifiability” was part of the history of Indian logic and Greek techniques of falsification. For example, the modus tollens principle was already known in Greece and India at a very remote time later.
The debate between rationalists and empiricists
René Descartes began his famous Discourse on Method with the phrase “Common sense is the best shared thing in the world” in which he identifies common sense with “reason” which he conceives as a human faculty which is the source of truth. Other philosophers such as Spinoza, Leibniz and Émilie du Châtelet accepted that there is a reliable source of knowledge, called reason, in human nature. This view, called rationalism, was criticized by empiricists (from England) such as Bacon, Locke and Hume. These empiricists argued that knowledge comes rather from observation. Whereas for Descartes it is irrational to support a position which cannot be deduced from a clear and distinct idea, for an empiricist it is rather to support a position which cannot be deduced from an observation which is irrational. This duality between rationalism and empiricism is, according to Vanzo, an oversimplification of the history of philosophy which was used by Kant to explain a philosophy which appears as a synthesis of the two extremes. Popper, who was greatly influenced by Kant, would also say that the deductivist-empirical theory he upheld can be seen as a synthesis of the two classical theories of knowledge: a synthesis of elements of rationalism and empiricism, and proposes to call it critical rationalism: the rational appears in the use of mathematics which, through a deductive logic, leads to the definition of empirical tests submitted to critical discussion. Like Peirce before him, because of the empirical component and the limitations of deductive logic, he adopts a fallibilist rationalism, i.e., without justification, except success in severe tests. According to Popper, these tests can refute the other theories considered, thus leaving the theory as the only possible candidate, but fundamentally everything passes through a synthesis of creativity and refutation and not through confirmation. Hume had highlighted the difficulty of justifying knowledge by observation. Hume explained our acceptance of laws by psychological mechanisms. This approach, called psychologism, will be rejected by Popper and will fuel the debate between objectivists and subjectivists.
(Includes texts from Wikipedia translated and adapted by Nicolae Sfetcu)