Are all swans white? The classical view of the philosophy of science is that it is the goal of science to "prove" such hypotheses or induce them from observational data. This seems hardly possible, since it would require us to infer a general rule from a number of individual cases, which is logically inadmissible. However, if we find one single black swan, logic allows us to conclude that the statement that all swans are white is false. Falsificationism thus strives for questioning, for falsification, of hypotheses instead of proving them.Falsifiability or refutability is the logical possibility that an assertion can be contradicted by an observation or the outcome of a physical experiment. That something is "falsifiable" does not mean it is false; rather, that if it is false, then some observation or experiment will produce a reproducible result that is in conflict with it.
For example, the claim "atoms do exist" is unfalsifiable: Even if all observations made so far did not produce an atom, it is still possible that the next observation does. In the same way, "all men are mortal" is unfalsifiable: Even if someone is observed who has not died so far, he could still die in the next instant "All men are immortal," by contrast, is falsifiable, by the presentation of just one dead man. Not all statements that are falsifiable in principle are falsifiable in practice. For example, "it will be raining here in one million years" is theoretically falsifiable, but not practically so.
The concept was made popular by Karl Popper, who, in his philosophical criticism of the popular positivist view of the scientific method, concluded that a hypothesis, proposition, or theory talks about the observable only if it is falsifiable. Popper however stressed that unfalsifiable statements are still important in science, and are often implied by falsifiable theories. For example, while "all men are mortal" is unfalsifiable, it is a logical consequence the falsifiable theory that "every man dies before he reaches the age of 150 years". Similarly, the ancient metaphysical and unfalsifiable idea of the existence of atoms has led to corresponding falsifiable modern theories. Popper invented the notion of metaphysical research programs to name such unfalsifiable ideas. In contrast to Positivism, which held that statements are senseless if they cannot be verified or falsified, Popper claimed that falsifiability is merely a special case of the more general notion of criticizability, even though he admitted that empirical refutation is one of the most effective methods by which theories can be criticized.
Falsifiability is an important concept within the creation-evolution controversy, where proponents of both sides claim that Popper developed falsifiability to denote ideas as unscientific or pseudoscientific and use it to make arguments against the views of the respective other side. The question of what can legitimately be called science and what cannot be legitimately called science is of major importance in this debate because US law says that only science may be taught in public school classes. Thus, the controversy raises the issue whether, on the one hand, creationistic ideas, or at least some of them, or at least in some form, may be legitimately called science, and, on the other hand, whether evolution itself may be legitimately called science. Falsifiability has even been used in court decisions in this context as a key deciding factor to distinguish genuine science from the nonscientific.
