Idiographic and Nomothetic Theory
Theory comes in two basic sizes: elemental, or idiographic theory and generalizing or nomothetic theory. An idiographic theory accounts for the facts in a single case. A nomothetic theory accounts for the facts in many cases. The more cases that a theory accounts for, the more nomothetic it is.
The distinction was first made by Wilhelm Windelband, a philosopher of science, in 1894. By the late 1800s, Wilhelm Dilthey’s distinction between the Naturwissenschaften and Geisteswissenschaften—the sciences of nature and the sciences of the mind—had become quite popular. The problem with Dilthey’s distinction, said Windelband, was that it couldn’t accommodate the then brand-new science of psychology. The subject matter made psychology a Geisteswissenchaft, but the discipline relied on the experimental method, and this made it a Naturwissenschaft.
What to do? Yes, said Windelband, the search for reliable knowledge is, indeed, of two kinds: the sciences of law and the sciences of events, or, in a memorable turn of phrase,
‘‘the study of what always is and the study of what once was.’’ Windelband coined the terms idiographic and nomothetic to replace Dilthey’s Natur- and Geisteswissenschaften.
Organic evolution is governed by laws, Windelband observed, but the sequence of organisms on this planet is an event that is not likely to be repeated on any other planet. Languages are governed by laws, but any given language at any one time is an event in human linguistic life. The goal of the idiographic, or historical sciences, then, is to deliver ‘‘portraits of humans and human life with all the richness of their unique forms’’ (Windelband 1998 :16).
Windelband went further. Every causal explanation of an event—every idiographic analysis, in other words—requires some idea of how things happen at all. No matter how vague the idea, there must be nomothetic principles guiding idiographic analysis.
Windelband’s formulation is a perfect description of what all natural scientists— vulcanologists, ornithologists, astronomers, ethnographers—do all the time. They describe things; they develop deep understanding of the cases they study,and they produce explanations for individual cases based on nomothetic rules. The study of a volcanic eruption, of a species’ nesting habits, of a star’s death is no more likely to produce new nomothetic knowledge than is the study of a culture’s adaptation to new circumstances. But the idiographic effort, based on the application of nomothetic rules, is required equally across all the sciences if induction is to be applied and greater nomothetic knowledge achieved.
Those efforts in psychology are well known: Sigmund Freud based his theory of psychosexual development on just a few cases. Jean Piaget did the same in developing his universal theory of cognitive development, as did B. F. Skinner in developing the theory of operant conditioning.
In anthropology, Lewis Henry Morgan (1877) and others made a brave, if ill-fated effort in the 19th century to create nomothetic theories about the evolution of culture from the study of cases at hand. The unilineal evolutionary theories they advanced were wrong, but the effort to produce nomothetic theory was not wrong. Franz Boas and his students made clear the importance of paying careful attention to the particulars of each culture, but Leslie White (1959) and Julian Steward (1949, 1955) did not reject the idea that cultures evolve. Instead, they advanced more nuanced theories about how the process works.
Steward (1955) chose just a handful of cases when he developed his theory of cultural evolution. Over time, data from Tehuacan, Mexico, and Ali Kosh, Iran—6,000 miles and several thousand years apart—support Steward’s nomothetic formulation about the multistage transition from hunting and gathering to agriculture. (The sequences appear to be similar responses to the retreat of the last glacier of the Paleolithic.) As we get more comparisons, the big picture will either become more and more nomothetic or it will be challenged.
And the effort goes on. Wittfogel (1957) developed his so-called hydraulic theory of cultural evolution—that complex civilizations, in Mexico, India, China, Egypt, and Mesopotamia developed out of the need to organize the distribution of water for irrigation— based on idiographic knowledge of a handful of cases. David Price (1995) studied a modern, bureaucratically organized water supply system in the Fayoum area of Egypt. The further downstream a farmer’s plot is from an irrigation pump, the less water he is likely to get because farmers upstream divert more water than the system allows them legally to have. Price’s in-depth, idiographic analysis of the Fayoum irrigation system lends support to Wittfogel’s long neglected theory because, says Price, it shows ‘‘how farmers try to optimize the disadvantaged position in which the state has placed them’’
(1995:107-108). Susan Lees (1986) showed how farmers in Israel, Kenya, and Sudan got around bureaucratic limitations on the water they were allotted. We need much more idiographic analysis, more explanations of cases, to test the limitations of Wittfogel’s theory. (See Harrower  for recent archeological work in southern Arabia on the role of irrigation systems in state formation.)