So observations have two purposes in Popper's view. On the methodological side, observations can be used to show that a law is false, which Popper calls falsification. On the logical side, observations, which are purely logical constructions, do not show a law to be false, but contradict a law to show its falsifiability. Unlike falsifications and "free from the problems of falsification", these contradictions establish the value of the law, which may eventually be corroborated. He wrote that an entire literature exists because this distinction was not understood.