“Profit is a subject to which economists have addressed themselves for at least two hundred years, but without much success. For there is at the moment no general theory of profits which commands anything approaching universal acceptance either among academic economists or among men of affairs.” (A. Wood)

“His Collected Writings show that Keynes wrestled to solve the Profit Puzzle up till the semi-final versions of his General Theory but in the end he gave up and discarded the draft chapter dealing with it.” (G. Tómasson and D. Bezemer)

“A satisfactory theory of profits is still elusive.” (M. Desai, New Palgrave Dictionary)
"In the practical affairs of trade, industry and finance no concept is more fundamental or more familiar than profit. Yet to the questions what profit is, and by what causes it is shaped and determined, economic science has not as yet supplied answers which command general agreement." (R. G. Hawtrey)
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“'What determines profits?' is a key question for understanding how our economy works.” (H. Minsky)

“... one of the most convoluted and muddled areas in economic theory: the theory of profit.” (P. Mirowski)
“We need to know what profits have been, how they have been made, to what uses they have been put, ...: no light on these matters is shed by the analyses of value, of utility and disutility, that have preoccupied so many of us for so long.“ (C. Parry)
"Much of what is usually offered as profit theory will be seen to be without merit." (M. Obrinsky)
"But in my opinion contemporary profit theory is floundering in eclecticism and has lost touch with the major economic changes of the past twenty-five years. Until we have clearly established what it is we are talking about, what we say is not going to have much value." (P. Bernstein)
"Profit theory has been largely concerned with specifying and isolating the 'function' for which profit is the 'reward.' This is scientifically irrelevant." (A. Murad)

"Of all the traditional branches of economics, the theory of profits has had the greatest difficulty in attaining the "safe path of a science." Our knowledge of the causes determining value, or wages, is indeed incomplete; but in these fields we do not find, and have not found for some considerable time, that fundamental disagreement among competent writers about the mere direction of approach, or that utter failure of promising lines of inquiry to yield results of any great importance, which Kant declared to be the marks of a science still groping in the dark." (J. R. Hicks)
"Nor do the modern variants add anything whatever on this score. For Debreu profits are simply a nonissue, while Arrow and Hahn make only passing reference to profits — and that only as a historical introduction. Whatever may be the usefulness of these idealized theoretical constructs, they cannot be said to throw any light on the profit issue; surely, therefore, they fail to capture the essence of a capitalist market economy." (M. Obrinsky)
Profit is the pivotal concept for the analysis of how the economy works. Without a correct profit theory, economics is vacuous. The conventional profit theory is logically indefensible. It is a unique fact of the history of economic thought that neither Classicals, nor Walrasians, nor Marshallians, nor Keynesians, nor Marxians, nor Institutionalists, nor Monetary Economists, nor Austrians, nor Sraffaians, nor Evolutionists, nor Game theorists, nor Econophysicists, nor RBCers, nor New Keynesians, nor New Classicals ever came to grips with profit. Hence they 'fail to capture the essence'. There are many opinions but no scientific understanding of the market economy, neither on the national nor on the global level. Rational economic policy or the implementation of a rational economic order is, therefore, a priori impossible. Economists have no true conception of the most important phenomenon in their universe.