In the twentieth century, the philosophy of science had many ups and downs. Karl Pauper, the renowned philosopher, was a staunch advocate of logical-prescriptive philosophy of science. The two pillars of his philosophy were realism and critical rationalism. Pauper did not believe in relativism, which to him was a kind of disease. He spoke of attaining the truth or verisimilitude. The philosopher of science after Pauper, specially Thomas Kuhn, Imre Lakatos and Paul Feyerabend did not follow his ideals and turned instead to the historical-descriptive philosophy or science. This article is an attempt to introduce the Views of these three philosophers and to explain the relationship between them and Pauper and philosophy of science.