What is Popper’s demarcation criterion for science?
For Karl Popper, falsifiability was the key criterion which distinguishes science from non-science, whether in the form of metaphysics or in the form of pseudoscience. In this he was reacting to and modifying the sort of criteria that the logical positivists used for demarcating science from metaphysics. For the logical positivists, the criteria was that of empirical testability. The positivists had advanced a verifiability theory of meaning. For them, a statement is meaninful it it is possible for us to specifiy the method by which it can be verified or refuted in terms of empirical observations. If a statement cannot be verified or refuted in that manner, then the positivists said that statement was metaphysical, and hence, in their view, lacking in cognitive meaning. Karl Popper disagreed with this approach. He was, in contrast with the positivists, not antimetaphysical. He regarded metaphysics, or at least certain varieties of metaphysics to be a legitimate area of philosophical study. Nor was he phased by the idea (presented by many other critics of logical positivism) that science itself is based on certain metaphysical assumptions. He agreed that it was and saw nothing wrong with that.
Another area of disagreement that Popper had with the logical positivists was over induction. Back in the 18th century, David Hume suggested that induction rested on shaky foundations. The principle of induction, for Hume, was something that could neither be proven by pure reason nor could it be established on the basis of experience. Empiricist philosophers after Hume continued to be bedeviled by the problem of induction. Popper, in contrast, proposed that the problem of induction could be solved, or rather dissolved, by showing that science is in fact not based on induction at all. According to Popper, scientific theories and hypotheses can never be proven to be true. They could be refuted or falsified on the basis of empirical observations. But even if a hypothesis should survive the most rigorous experimental testing, that sitll does not prove it to be true. At most, this show that the hypothesis has been corroborated. It is always possible that it might be refuted by future observations.
Given the above reasons, Popper proposed substituting his principle of falsifiability for the positivists’ verifiability principle. First of all, in contrast with the positivists, his falsifiability principle was not a theory of meaning. Theories that are not, even in principle, falsifiable, can be labeled metaphysical, but that did not make them meaningless.
Popper used his principle of falsifiability to attack what he saw as the scientific pretensions of Marxism and psychoanalysis, neither of which he regarded as being legitimate sciences.
He viewed Marxism, as presented in the work of Marx & Engels, had originally been scientific. In other words, he took Marx and Engels as having attempted to present theories that were empirically testable and falsifiable. But, he argued, that as predictions made by Marx & Engels were falsified, later generations of Marxists added to these theories ad hoc hypotheses that saved the theories from refutation, but at the cost of stripping them of their original scientific status.
In the case of psychoanalysis, Popper argued that it was unfalsifiable from the get-go. Thus, it was never a real science.
