Judy L. Klein
There are few tools so important to economic pedagogy and analysis as graphic representation. Even a cursory comparison of economics with other social and natural sciences reveals the unusual emphasis economists place on the use of diagrams. Yet, little has been written on economists as graphic toolmakers. This exploration of early developments in economists’ use of graphs addresses the temporal conjunctures of graphs and economic concepts, the developmental patterns of common forms of economic diagrams, comparisons with diagrams used in other modes of thought, and the significant contributions of economists to the technique of visual abstraction.
The process by which I examine these tools involves weaving the source of the raw material of graphs with the relevant time frame (see Table 6.1). Henry Cunynghame in A Geometrical Political Economy, published in 1904, classified diagrams as law-curves or fact-curves. The raw materials for law-curves are hypotheses and mental abstractions; the raw materials for fact-curves are concrete data. I have woven the law-curve/fact-curve distinction with a time-frame distinction, made by Joan Robinson (1980), between curves drawn in logical time and those in historical time. Lines imaged in logical time connect and compare static positions. The sense of logical time is created by the eye moving left to right from lower to higher values of the x variable. One can also go in the reverse direction in logical time, whereas the curves
Table 6.1 Class sification of graphs
Mental abstractions drawn to compare values of y as value of x is low or high
Actual data plotted to compare values of y as value of x is low or high
Mental abstractions drawn to follow path or y changing over time
Actual data plotted to follow path of y changing over time