Splitters and lumpers

Lumpers and splitters are opposing factions in any discipline that has to place individual examples into rigorously defined categories. The lumper-splitter problem occurs when there is the need to create classifications and assign examples to them, for example schools of literature, biological taxa and so on. A "lumper" is an individual who takes a view of a definition, and assigns examples broadly, assuming that differences are not as important as signature similarities. A "splitter" is an individual who takes precise definitions, and creates new categories to classify samples that differ in key ways.

The earliest use of these terms was by Charles Darwin, in a letter to J. D. Hooker in 1857, "(Those who make many species are the 'splitters,' and those who make few are the 'lumpers.')" They were introduced more widely by George G. Simpson in his 1945 work "The Principles of Classification and a Classification of Mammals." As he put it, "splitters make very small units – their critics say that if they can tell two animals apart, they place them in different genera … and if they cannot tell them apart, they place them in different species. … Lumpers make large units – their critics say that if a carnivore is neither a dog nor a bear, they call it a cat."

Another early use can be found in the title of a 1969 paper by the medical geneticist Victor McKusick: "On lumpers and splitters, or the nosology of genetic disease."

Reference to lumpers and splitters also appeared in a debate in 1975 between J. H. Hexter and Christopher Hill, in the Times Literary Supplement. It followed from Hexter's detailed review of Hill's book Change and Continuity in Seventeenth Century England, in which Hill developed Max Weber's argument that the rise of capitalism was facilitated by Calvinist Puritanism. Hexter objected to Hill's 'mining' of sources to find evidence that supported his theories. Hexter argued that Hill plucked quotations from sources in a way that distorted their meaning. Hexter explained this as a mental habit that he called 'lumping'. According to him, lumpers rejected differences and chose to emphasize similarities. Any evidence that did not fit their arguments was ignored as aberrant. Splitters, by contrast, emphasised differences, and resisted simple schemes. While lumpers consistently tried to create coherent patterns, splitters preferred incoherent complexity.

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