Karl Popper and the Falsification of Scientific Theories

"Irrefutability of a theory is not a virtue (as people often think) but a vice." -- Karl Popper

What is science? What makes it different from pseudo-science? These and related questions stem from the demarcation problem -- the problem of identifying the conditions necessary for some theory or methodology to be regarded as science. A very common answer to the demarcation problem, writes Karl Popper, goes something like this:

C: "...science is distinguished from pseudo-science -- or from 'metaphysics' -- by its empirical method, which is essentially inductive, proceeding from observation or experiment" [1].

Popper finds C to be unsatisfactory as a solution to the problem of demarcation (more on why he thinks so below). Instead, Popper offers the following solution:

The Criterion of Falsifiability: some theory, T, is a scientific theory if it can, in principle, be falsified.

Popper writes, "The criterion of falsifiability is a solution to this problem of demarcation, for it says that statements or systems of statements, in order to be ranked as scientific, must be capable of conflicting with possible, or conceivable, observations." Consider some theory, T. If T is a falsifiable theory, argues Popper, it is so because it makes "risky" predictions; that is, it leads us to expect reality to be a certain way. If our observations show us that reality isn't the way T has led us to expect, then T is falsified (or, more mildly, disconfirmed). Having this feature, argues Popper, makes a theory scientific.

THE MOTIVATION FOR FALSIFIABILITY

The worry that led Popper to endorse this criterion as a solution to the demarcation problem was that many theories seemed capable of being confirmed by a large assortment of phenomena, as well as appearing consistent with nearly all relevant discoveries, but seemed to avoid the potential for falsification. Isn't that what we want in a theory? Not quite. Confirmation is cheap when one's theory cannot admit of any potential falsifiers. Marc Alspector-Kelly expresses the problem as follows: "Confirmation is easy to come by, so long as the theory is so formulated as to render it immune to refutation. But then the victory of confirmation, where no disconfirmation is possible, is empty: if a theory takes no risks, then the fact that it suffers no defeat can command no respect" [2]. Any theory can be confirmed by various phenomena if it is vague enough, continuously defended by ad hoc hypotheses, or sufficiently elastic so as to accommodate any conceivable feature of reality. Their vagueness and elasticity, Popper thinks, are also responsible for their unfalsifiable and, as a consequence, for their unscientific nature. He writes, "A theory which is not refutable by any conceivable event is nonscientific."

Popper critiqued astrology (not to be confused with astronomy), Freudian psycho-analysis, Alderian psycho-analysis, and Marx's theory of history on the grounds that they lacked falsifiability. Here is a key example revealing Popper's concern:

"I may illustrate this by two very different examples of human behavior: that of a man who pushes a child into the water with the intention of drowning it; and that of a man who sacrifices his life in an attempt to save the child. Each of these two cases can be explained with equal ease in Freudian and in Adlerian terms. According to Freud the first man suffered from repression (say, of some component of his Oedipus complex), while the second man had achieved sublimination. According to Adler the first man suffered from feelings of inferiority (producing perhaps the need to prove to himself that he dared to rescue the child). I could not think of any human behavior which could not be interpreted in terms of either theory. It was precisely this fact -- that they always fitted, that they were always confirmed -- which in the eyes of their admirers constituted the strongest argument in favor of these theories. It began to dawn on me that this apparent strength was in fact their weakness."

GOOD THEORIES, TESTING, AND THE GOAL OF SCIENCE

The following points are some of Poppers insights on what counts as a good theory and what counts as a legitimate test of a theory:

(1) "Every 'good' scientific theory is a prohibition: it forbids certain things to happen. The more a theory forbids, the better it is."
(2) "Confirmations should only count if they are the result of risky predictions..."
(3) "Every genuine test of a theory is an attempt to falsify it, or to refute it. Testability is falsifiability..."

Championing the principle of falsification as the torch to illuminate the darkened world of scientific conjecture, Popper concludes that science should be an enterprise solely interested in making conjectures about reality and then subjecting those conjectures to refutation. While a theory can be corroborated by various things, to look for confirmation is not what a scientist is ultimately after (remember, confirmation is easy to come by, Popper thinks). What we want is to rid ourselves of false conjectures by sifting them through the mesh of refutation. He writes, "The critical attitude may be described as the conscious attempt to make our theories, our conjectures, suffer in our stead in the struggle for the survival of the fittest. It gives us a chance to survive the elimination of the an inadequate hypothesis...We thus obtain the fittest theory within our reach by the elimination of those which are less fit. (By 'fitness' I do not mean merely 'usefulness' but truth;...)."

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[1] Popper, Karl. "Science: Conjectures and Refutations." Philosophy of Science: An Historical Anthology. Ed. Timothy J. McGrew, Marc Alspector-Kelly, and Fritz Allhoff. N.p.: Blackwell, 2009. Print. (all subsequent quotes are from the same source unless otherwise specified).
[2] Philosophy of Science: An Historical Anthology. Ed. Timothy J. McGrew, Marc Alspector-Kelly, and Fritz Allhoff. N.p.: Blackwell, 2009. Print.