The inability both to understand and to predict the financial and economic crisis of the first decade of this century has seriously damaged the reputation of the mainstream macroeconomics (cf. Stiglitz, 2015). Mainstream macroeconomists have tried then to defend themselves arguing that severe crises are essentially unpredictable, for otherwise they would not cause such a high degree of distress (cf. Caballero, 2010).

By contrast, in this paper, I try to argue that the reasons for the over cited  inabilities by mainstreamers and the subsequent lack of “reputation” may be founded on 2 analytical implicit or explicit conditions adopted in their analysis:

1. Conventional approaches in macroeconomics have, for a long time, neglected the relevance on the real variables of the financial structure (that is, they have focused upon a “real exchange economy” rather than a true “monetary economy”, using Keynes’s terminology);

1. When they have included the financial markets in their analysis they have embraced the results of the  Efficient Market Hypothesis (EMH).

The aim is to show how, as soon as the focus is on the analysis of a modern capitalist economy as a “true” “monetary economy” and if the EMH is scrutinized critically, taking into account the complexity of the financial system (Sau, 2013), a true paradox stemmed from a theoretical point of view:  finance and credit are essential for the functioning of the macroeconomic system but, in absence of adequate economic policies,  they are  also the seeds of the endogenous process that conduct to instability and to great financial crisis as stressed by H. P. Minsky since 80s.