Marjorie Shepherd Turner in Joan Robinson And The Americans has a good description of the useless nature of economic diagrams in general:

Robinson saw general equilibrium, then, as a block to appropriate analysis, for it had assumed away the economic problems. She objected to economists who admired equilibrium analysis for its “logical elegance and completeness” even though they knew it was “useless”: “Human life does not exist outside history and no one has correct foresight of his own future behavior, let alone of the behavior of all the other individuals which will impinge upon his. I do not think that it is right to praise the logical elegance of a system which becomes self-contradictory when it is applied to the question that it was designed to answer.”²⁵

On the other hand, Robinson reserved the right to compare positions of equilibrium “each with its own past and its own expectations about the future.” She complained that American economist “Dr. Findlay” (Ronald Findlay) failed to recognize the difference between such a comparison of existing positions and “the analysis or a process going on through time, with expectations changing.²⁶

To the end or her life she believed that “mainstream teaching” had “been inculcating defective methodology,” especially in the United States:

The exposition both of general equilibrium and of long-run accumulation seems generally to be conducted by drawing a two-dimensional diagram on a black-board and then introducing historical events into it. A change cannot be depicted on the plane surface or the blackboard. Changes occur in time, and as soon as a point moves off the blackboard into the third dimension of time, it is no longer bound by the relationships shown in the diagram.²⁷

Robinson was particularly critical or Samuelson who, as a mathematician,

… knows that a functional relationship is timeless and makes no reference to history or to the direction of change … However, Professor Samuelson continues to use his construction to describe a process or accumulation that raises wages, alters technology, and changes a stock or inputs made, say, or wood into one made of iron and then into copper … To Kornai. Harcourt, and myself, this methodology is unacceptable, but Professor Samuelson assures us that it is quite all right.”²⁸

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Endnotes

25. JR 1978a:126-136.
26. CEP 3:50.
27. CEP 5:69. Elsewhere in the article (60), JR associated mainstream teaching with the United States.
28. CEP 5:88. Samuelson feels that JR refused to understand what he was arguing. Samuelson Interview 1985 and see Chapter 10.

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References

Robinson, Joan
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⸻ (1965a) Collected Economic Papers vol. 3. Oxford: Basil Blackwell 1975.
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⸻ (1978a) Contributions to Modern Economics, New York: Academic Press.
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⸻ (1979g) Collected Economic Papers vol. 5. Oxford: Basil Blackwell 1980.
Reprinted by MIT Press.