The capacity for language is a defining property of our species, yet despite decades of research, evidence on its neural basis is still mixed and a generalized consensus is difficult to achieve. We suggest that this is partly caused by researchers defining “language” in radically different ways, with focus on a wide range of phenomena, properties, and levels of investigation. Accordingly, there is very little agreement amongst cognitive neuroscientists of language on the operationalization of fundamental concepts to be investigated in neuroscientific experiments. This paper reviews chains of derivation in the cognitive neuroscience of language, focusing on how the hypothesis under consideration is defined by a combination of theoretical and methodological assumptions. We first attempt to disentangle the complex relationship between linguistics, psychology, and neuroscience in the field. We then focus onhow conclusions that can be drawn from any experiment are inherently constrained not just by the research techniques and analyses adopted, but also by the theoretical starting point of the study: auxiliary assumptions, both theoretical and methodological,on which the validity of conclusions drawn rely. These issues are discussed in the context of classical experimental manipulations, as well as study designs that employ novel approaches such as naturalistic stimuli and computational methods. We conclude by proposing that a highly interdisciplinary field such as the cognitive neuroscience of language requires researchers to form explicit statements concerning the theoretical definitions, methodological choices, and other constraining factors involved in their work.