Recent discussions of the taxonomy of the Pantherophis obsoletus complex (Burbrink et al. 2020, 2021; Hillis and Wüster 2021) have highlighted a need for a clarification of the terms monophyly and paraphyly as they are commonly applied to species and higher taxa, respectively. These definitions, and their application to biological taxonomy, are critical to delimitation and recognition of species within this complex of snakes (as well as many other biological taxa). Although these concepts have been the subject of much previous discussion (e.g., Niegel and Avise 1986; Pamilio and Nei 1988; McKitrick and Zink 1988; Patton and Smith 1994; Baum and Shaw 1995), a brief review is needed to respond to the arguments of Burbrink et al. (2021).