What is Intuitive Taxonomic Practice?

Scotland and Steel (2015) recently explored the idea of character compatibility, examining the issue from the perspective of a particular model, "a simple and extreme model in which each character either fits perfectly on some tree, or is entirely random $\ldots$,." (Scotland and Steel 2015, p. 492, abstract). They suggested that character compatibility, when formalized as a phylogenetic method, captured what they believed was the "intuitive taxonomic practice of recognizing taxa based on conserved nonhomoplastic characters" (Scotland and Steel 2015, p. 493). Although we agree that there is much to be said for compatibility analysis, and "it has largely been set aside, initially in favour of maximum parsimony, and, more recently, by model-based methods for inferring phylogeny from DNA sequence data" (Scotland and Steel 2015, p. 493), their use of the expression "intuitive taxonomic practice" attracted our attention. Below we discuss in more detail what "intuitive taxonomic practice" might be and relate that understanding to recent progress in the history of biology, specifically the history of systematics (taxonomy), and finally sketch out a proposal that might satisfy those of us who retain an interest in capturing in a more rigorous way what "intuitive taxonomic practice" might have been. [Compatibility methods; monothetic taxa; polythetic taxa."History is what we have to struggle to remember even when legend [myth] is more pleasing" (Adam Gopnik, The New Yorker, 23 November 2015).