Context
The historical context of the first half of the 20th century can shed light on Karl Popper's ideas. When Popper wrote the draft of The Logic of Scientific Discovery (1934), he wanted to publish a book that would offer his family of Jewish descent the opportunity of leaving Austria before Nazism took hold there, since he could then opt for a university post in other countries. He finished the book in 1934 and obtained a post at Canterbury University, New Zealand in 1937. Germany annexed Austria in 1938.
In the early to mid-20th. century Europe experienced a scientific boom. Popper lived in a time of automatic transmissions, televisions and the atomic bomb. There was a revival of racist propaganda, presented as a false branch of scientific study called eugenics, which had been introduced by Galton in the previous century. Positivistic methods and extreme ideologies meant that evidence was manipulated and interpreted to justify political beliefs.
Physics had undergone a profound change in the years previous to the publication of Popper's book. Einstein had published his paper on special relativity and Bohr had created a model that described the structure of atoms. Related to these novel ideas was the rise of quantum theory, which analysed the transference of energy at atomic and subatomic levels. The 'Copenhagen interpretation' announced that certain classical ideas of position and speed did not hold at the subatomic level as they did at the macroscopic level. Another physicist added that the position and velocity of an object were not simultaneously measurable with exact precision. This is known as the "Heisenberg uncertainty principle".
As a result of these theories traditional knowledge about space, time and causality was under question, as was what can be known through empirical experimentation. Popper referred to some of these results in modern physics. He discussed probability and offered a critique of the Heisenberg principle, suggesting that phenomena at the microscopic level may be more measurable than physicists assume. He also addressed the basic problem of scientific knowledge posed by 20th. century physics when empirical results deviate so far from traditional ideas on space, time and causality.
In his book Popper was also reacting against logical positivism, which maintained that the only form of factual knowledge is scientific knowledge. One of the precursors of logical positivism was the Austrian thinker Ernst Mach (for whom the Mach number is named). After Mach died a group of logical empiricists gathered in Vienna, led by the German philosopher Rudolf Carnap. Popper argued that logical positivists accepted scientism, a worldview that only admits empirical science as truth, while rejecting religious and metaphysical claims. Popper held that metaphysical statements were meaningful, but they should be distinguished from scientific theories.
Summary
Preface
The 1959 English edition preface reiterates the points made in the 1934 German Preface: the differences between science and philosophy. Scientists investigate within a previous structure of theories that permits the definition of problems; philosophers face a "heap of ruins" and must begin by determining what their problem is. However, some philosophers
"still... believe that philosophy can pose genuine problems about things."
Against modern opinion Popper argues that all philosophical problems are not actually linguistic or definition issues. He maintains that the philosophical method is the same as natural sciences and intends to study the problem of scientific knowledge:
"Stating one's problem clearly and ... examining its various proposed solutions critically."
The author also criticises the model languages' construction approach where statements are analysed. He thinks it too artificial to deal with scientific progress.
Part 1 Introduction to the Logic of Science
Chapter 1 A Survey of Some Fundamental Problems. The problems of scientific inquiry addressed are: how is it acquired?, what does it consist of?, how is it tested? Popper then suggests a simple way of distinguishing scientific statements from others. He affirms that a statement can only be accepted as scientific if it is falsifiable by experience.
Chapter 2 On the Problem of a Theory of Scientific Method. The author argues against critics who only seek a logical description of science rather than the application of scientific thinking methods.
Part 2 Some Structural Components of a Theory of Experience
Chapter 3 Theories, elaborates on the logical structure and principles common to all scientific theories.
Chapter 4 Falsifiability demonstrates that while methodological decisions are used as a base, falsifiability can be meaningfully applied within this structure.
Chapter 5 ("The Problem of the Empirical Basis") The author argues that statements of science cannot be inferred from sensory observations since these are full of theories and so are less basic than they appear to be.
Chapter 6 Degrees of Testability submits a way of testing various scientific theories within the framework of falsifiability.
Chapter 7 Simplicity indicates how this framework includes seeking scientific theories that are as simple as possible.
Chapter 8 Probability is a description of how the author's theory of scientific knowledge can account for probabilistic hypotheses.
Chapter 9 Some Observations on Quantum Theory deals with how falsifiability and probability are applicable to quantum physics.
Chapter 10 Corroboration, or How a Theory Stands Up to Tests. Popper believes that a theory can never be positively verified and he addresses the question of how theories can be corroborated. He also develops the links between falsifiability and formal logic.
Appendices
Popper elaborates on arguments in the book and responds to criticism. Several appendices present his probability theory in mathematical terms; others critique the principle of induction, which Popper rejects as a basis for scientific knowledge. The final appendix introduces a letter from Einstein questioning some of Popper's examples and proposes clarifications.
Themes
Falsifiability
Falsifiability means that a scientific statement must be disprovable in principle, through observation or experiment. For example, the assertion: "All planets move in circular orbits" is disprovable because if one planet is observed not to have a circular orbit, the statement is demonstrably false.
Popper's falsifiability criterion contradicts positivism, a long tradition of thought which emphasises the verifiability of statements. Both approaches differ in the expected results of tests. Positivism holds that experiments can confirm or reject a theory as true or false. Popper argues that many theories can be refuted through experiment, but that all theories are impossible to prove. He affirms that no scientific statement can attain a standard that no statement about the natural world can reach.
The author offers a concrete example in the observation: 'all swans are white'. Positivists would maintain that the more white swans are seen, the more likely the truth of the affirmation. On the other hand, Popper agrees that it is good to prefer theories which have not yet been falsified, yet it is impossible to verify a theory, even in principle. The observation of just one black swan would falsify the original statement and no number of white swan sightings could ever make the statement more probable. His argument is not that non-falsifiable statements are meaningless, rather that they are unscientific. The falsifiability criterion is not about meaningfulness against meaninglessness or usefulness against uselessness, but a distinction between scientific and nonscientific.
Induction
The 18th. century empiricists addressed the traditional problem of how knowledge could arise from individual experiences. They embraced induction as an answer, with its meaning that reasoning can generalise conclusions based on specific instances. This process was incorporated as a principle of logical reasoning which considered probable and justifiable conclusions related to the number of observations in their favour. Popper objected that once the principle was accepted it became easier to rationalise the induction process that produced it. It was in this way that the white swan hypothesis became acceptable.
Popper rejects inductivism outright. He argues, for instance that:
"all the repetitions [that people] experience are approximate repetitions."
He adds that it is possible to induce all sorts of hypotheses from the same data simply by changing the definition of what is repeated. He also observes that the principle of induction cannot be empirically verified and depends on an inductive process to establish it.
The author adds caveats to his criticism. He admits induction in commonsense thinking, such as an assumption like 'the sun will rise tomorrow'. He also accepts mathematical induction, a proof strategy that uses established repetition in a maths structure. However, he objects to induction being raised to a rule of reasoning that can be applied to all thinking, especially scientific conclusions.
Corroboration
If falsifiability is accepted then scientific theories cannot be proven. So what is the point of scientific investigations? Popper replies that they can help corroborate a theory, even if they can't confirm it.
The author emphasises the notion that no amount of evidence can verify a theory definitively. The most we can expect is corroboration of a theory:
"The results of this experiment are compatible with the theory, i.e., they do not falsify it."
Metaphorically this approach is that of sculpturing in marble. The artist proceeds as in the unlikely story of Michaelangelo who is reported to have said that sculpting his David statue was easy since he just chipped away the marble that didn't look like David. Popper suggests that science should chip away false theories through experimentation. The resulting 'sculpture' is the edifice of scientific thought, which is built up of theories that have survived the chiselling.
Popper maintained that devising experiments to defend or confirm theories is a waste of time. The way to increase human knowledge is to demonstrate that a theory is false. This implies devising very stringent experiments to falsify a theory, not by logical deduction, but through a methodological decision.
Criticism of Popper's Thinking
Two lines of criticism emerged about Popper's The Logic of Scientific Discovery. One argues against his assumptions; the other sustains that he has mischaracterised scientific practice.
Those who are critical of his assumptions argue that his theory is based on a simplistic polarity between corroboration and falsification of hypotheses in empirical experiments.
The Hungarian, Lakatos, maintains that an observation does not necessarily falsify a theory through not corroborating it, but Popper's theory does not cover this possibility. The same author proposed a personal system, Methodology of Scientific Research Programs (MSRP), which is more flexible than Popper's, to define the particular characteristics of scientific thought.
In the US, the physicist, Sokal, and in Belgium, Bricmont's book Fashionable Nonsense: Postmodern Intellectuals' Abuse of Science (1997) suggest that falsifiability cannot alone be relied on to distinguish between a scientific and nonscientific theory. They give the example of the predictions of astrology and astronomy, which can be equally falsifiable, yet the latter is accepted as science, while the former is not.
Lakatos also objected to Popper's logic of falsifiability. He made the observation that theories were not rejected immediately a glitch was noticed, but were often retained as the nearest estimate. Copernicus' astronomy superseded the ancient Greek model of the universe, despite his failure to explain certain phenomena. Newton's law of gravity was accepted as a refinement of Copernicus, even though it left some questions unresolved. Lakatos maintained that a scientific model of knowledge must be able to accommodate partial advances.
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