Against that, Popper argued that the central property of science is falsifiability. All scientific claims can be proved false, at least in principle. If no such proof can be found despite sufficient effort, then the claim is likely true. Popper's ideas were applauded by many scientists (like Peter Medawar). However, sceptics noticed that theories were often not discarded when a prediction was refuted. The theory was simply adjusted to take into account the new findings. It was clear from this that, although falsifiability was important, it could not be a simple way to distinguish science from non-science.