JKH and Sandwichman have already left comments there.
There Isn’t Really a ‘Mainstream’ at All
J. W. Mason
In my estimation as a philosopher rather than an economist, there are two major influences that are overlooked in the conventional way of doing economics.
The first and most important is Marx in that he takes a wholistic approach based on system theory.
The general conclusion at which I arrived and which, once reached, became the guiding principle of my studies can be summarised as follows.
In the social production of their existence, men inevitably enter into definite relations, which are independent of their will, namely relations of production appropriate to a given stage in the development of their material forces of production. The totality of these relations of production constitutes the economic structure of society, the real foundation, on which arises a legal and political superstructure and to which correspond definite forms of social consciousness. The mode of production of material life conditions the general process of social, political and intellectual life. It is not the consciousness of men that determines their existence, but their social existence that determines their consciousness.…
In studying such transformations it is always necessary to distinguish between the material transformation of the economic conditions of production, which can be determined with the precision of natural science, and the legal, political, religious, artistic or philosophic – in short, ideological forms in which men become conscious of this conflict and fight it out. Just as one does not judge an individual by what he thinks about himself, so one cannot judge such a period of transformation by its consciousness, but, on the contrary, this consciousness must be explained from the contradictions of material life, from the conflict existing between the social forces of production and the relations of production. No social order is ever destroyed before all the productive forces for which it is sufficient have been developed, and new superior relations of production never replace older ones before the material conditions for their existence have matured within the framework of the old society.The second is Institutionalism, general attributed to Veblen as founder. Institutionalism is concerned with, "the totality of these relations of production [that] constitutes the economic structure of society, the real foundation, on which arises a legal and political superstructure and to which correspond definite forms of social consciousness."
Taking this into account, the proper study of economics encompasses the "relations of production appropriate to a given stage in the development of their material forces of production." Thus, the proper study of economics far exceeds the boundaries of most contemporary approaches to the discipline called economics.
Institutionalism rounds out Marx, who was of course cognizant only of the institutions of his day. Note that MMT is largely institutional in that modern money is chartal money or state money. Money is an integral aspect of modern legal institutions and in the US Constitution, the legislature is given institutional control, while legal interpretation is left to the courts.
The major problem with so-called conventional economics is the presumption, containing hidden assumptions, regarding the physical, biological and social system in which economic activity is occurring. As Samuelson noted, formalizing economics similar to natural science requires assuming an ergodic system in which economic behavior occurs. However, as even Marx realized well over a century ago, this system is actually a complex adaptive system that not only changes over time but is subject to emergence owing to reflexivity.
The dodgy assumption is revealed in another fundamental assumption employed in conventional economics — ceteris paribus. However, it needs to be shown in any specific case that all conditions other then the variable under scrutiny actually remain the same.
And as Sandwichman points out in a comment there, cet. par. is actually used selectively in order to further an argument, which is a logical fallacy that indicates either ignorance of cognitive bias or else sophistry.