Explanation in critical realism (CR) is based on the conduction of open critical analyses in three domains: empirical, actual and real, or deep. The scientific aim of CR is finding deep internal patterns of behavior for the explanation of phenomena. Critical realism, which later on will be used for grounding data in theory, must be based on an appropriate selection of data for their continuing comparison and approval in terms of topics, perspectives, assumptions, methods, and data. This permanent task is relevant for macro-finance, which is out of paradigm according to the post-Keynesian view since no orthodox explanations are offered about the generation mechanisms, irregularities or interconnections of the inherently and abruptly volatile financial sector. Financial events are volatile since the consequences of men activities are neither eternal nor ubiquitous. Therefore the standard explanation related to efficiency-rationality does not explain the main aspects of reality. In this sense the only regularity in finance is uncertainty, which possesses its own rationality and is hence real and susceptible to be researched in qualitative terms. In addition since money is an emerging property, financial interrelationships are complex. Hence analyses of the financial sector must take account of organicism and the existence of permanent and apparently unexplainable fluxes. Therefore a qualitative interpretation of real and dynamic-compared data, along with data triangulation must be conducted. In particular, the qualitative methods of interviews and documental analysis are to be used in this case study in finance related to the obtaining of qualitative information for explaining both volatility and irrationality in financial instruments and indices. On the other hand, the research by-product of historical investigation captures the gist of the development of finance. The aim is to do justice heterodox economics and finance by appropriately explaining the causes, interrelations and consequences of such issues as money, uncertainty, financial stability and the role of financial institutions in a case study of the Mexican Stock Market (BMV), an emerging market, which is highly susceptible to permanent volatility.