Edmund Gettier called into question the theory of knowledge and the traditional definition of knowledge. Gettier's argument is that there are situations in which one's belief may be justified and true, yet fail to count as knowledge. He contended that while justified belief in a true proposition is necessary for that proposition to be known, it is not sufficient. According to Gettier, there are certain circumstances in which one does not have knowledge, even when all of the above conditions are met. Gettier proposed two thought experiments, which have come to be known as "Gettier cases," as counter examples to the classical account of knowledge. He argued it is possible to arrive at an assumption based on belief which is deemed justified, but happens to be true only by chance, because the outcome was predicted for the wrong reason and so can't be classed to be knowledge.