Karl Popper argued that positivist sociologists were not really scientific in their approach to research because, instead of using deductive reasoning they used inductive reasoning. In other words, instead of subjecting their hypothesis to falsification, trying to find evidence to disprove it, they do the opposite: they try and find evidence that supports their hypothesis. The flaw with this approach is often illustrated with swans. If you had a hypothesis that "all swans are white" you would find more and more supporting evidence with every white swan you found. But the critical evidence is the black swan that proves your hypothesis incorrect.