Carl Menger is the founding father of the Austrian School of Economics with his landmark “Principles of Economics” (1871), which laid the intellectual groundwork for future Austrian scholars. One of the main themes of the book is the idea that the value of a good is not determined by factors that can be objectively determined (e.g. labour or material costs), but by subjective valuations of the good by individuals. In that sense Carl Menger can be seen (alongside Leon Walras and William Stanley Jevons) as one of the founders of marginalist economics, which is the bedrock for the whole body of modern economics.
Menger was a key participant as well in one of the most important battles concerning methods in the social sciences, the so-called “Methodenstreit” (dispute over methods). Menger’s intellectual opponents in the German Historical School argued against the existence of economic laws and accordingly did not see any role for the use of theory within economic research. Menger on the other hand did not deny the relevance of inductive-empirical methods, but was convinced that empirical analysis always had to be based on some sort of theoretical framework.
The course that economic science has taken since the late 19th century certainly proves Menger right.