In view of the fact that the methodology of economics is a seminal and significant field and professor Machlup is a prominent economist and a well known theoritician of methodology a brief elucidation may be worth while. Frits Machlup (1902-1983) wrote his doctoral dissertation under Von Mises (a pioneer of Austrian School). Ile lectured at the University of Vienna before going to America whereupon he taught at Johns Hopkins and Princeton universities. In 1971 he moved to Newyork university and remained there for the rest of his life. lie was elected president of "American Economic Association in 1967". Among his many contubutions to economics is his extensive research in the theory of firm and international economics (publishing 100 articles and 17 books on the subject). To teach economics to students more precisely, he addressed the issue of methodology of economics. The present paper is a Persian translation of one of 26 articles from his book "Methology of Economics and Other Social Sciences".