In modernity era, philosophical thoughts certainly have crucial influences on the growth and development of culture and civilization of western world. Among those philosophers who have theoretical viewpoints and opinions, and furthermore have introduced efficient methods in studying natural and human phenomena have more affection on interiorizing and making applicable philosophical thoughts in scientific, technological and cultural development of west. In this paper, two methodologies are discussed one of which is introduced in the beginning of modernity by leading French philosopher, Rene Descartes as a general and useful method for all kinds of sciences and the other one is introduced in heyday of modernity by famous Austrian philosopher, Karl Popper as a beneficial method for studying social phenomena. Evidently, each one of these methods is relying on particular principles and is derived from special ideological and historical backgrounds. They have also advantages and deficiencies which make them apt to be criticized. In this issue, the moot points above are reviewed and at the end, common aspects of both methods are considered briefly.