Briggs and Peck [in "Using Learning Progressions to Design Vertical Scales That Support Coherent Inferences about Student Growth"] call for greater care in the conceptualization of the target attributes of students, or "what it is that is growing from grade to grade." In particular, they argue that learning progressions can serve as valuable bases for the design of assessments and for the interpretation of assessment results, especially in terms of change over time (or "growth"). Against the backdrop of the history of science in general, it must be regarded as remarkable that Briggs and Peck's argument--the core of which is simply that the meaningfulness of claims regarding changes in an attribute depends on clarity about the attribute itself--could be regarded as at all novel. But against the backdrop of (especially, but not exclusively, U.S.-based) educational assessment and psychometrics, in which technical concerns have arguably been foregrounded at the expense of substantive and conceptual concerns, their contribution is valuable and timely. However, I believe their points can be productively pushed even further. In particular, I argue that even greater care can and should be taken in attending to (a) the distinction between claims about the actual state of affairs in the world and claims about the ways in which we choose to model or represent such affairs via our concepts and language and, relatedly, (b) the distinction between elements of our belief systems we take to be immune to revision (i.e., as "assumptions" or "stipulations") versus those taken to be open to revision (i.e., as "hypotheses"). [For "Using Learning Progressions to Design Vertical Scales That Support Coherent Inferences about Student Growth," see EJ1067453.]