This paper stresses the need for a sound conceptual specification of research constructs prior to fitting them to explanatory models. It emphasizes that in addressing the conceptual level of the predictive validity framework [Libby, R., Bloomfield, R., & Nelson, M. (2002). Experimental research in financial accounting. Accounting, Organizations and Society, 27, 775-810], special attention must be paid to two issues: (1) the production of a specific agreed-upon meaning and domain for each construct of interest; and (2) the specification and conceptual justification of the nature and direction of the epistemic relationships between constructs, dimensions and indicators (i.e., reflective vs. formative models; latent vs. emergent models). The paper highlights the importance of both issues especially in the case of practice-defined variables, and it provides guidelines on how to address both aspects of conceptual specification. While the issues raised are pertinent to many research areas, the paper concentrates on the implications for management accounting and control systems (MACS) research, using interactive use of control systems [Simons, R. (1995a). Levers of control. Boston: Harvard Business School Press] to illustrate how researchers should go about specifying meaning and epistemic relationships in MACS research.