What does it mean that an issue is conceptual in nature?

McGrath (2005/this issue) argues that "the conceptual complexity [italics added] of the constructs psychologists choose to measure and the scales they use to measure them has played an important role in the failure to develop more accurate measurement systems" (p. 112). Although we agree with this, we argue, in this commentary, that McGrath has misdiagnosed the source of these difficulties and that this misdiagnosis originates with an unresolved articulation of the nature of a conceptual issue and of the relationship between conceptual and empirical issues in science.