Quantifying What Is Efficacious Yet Not Observable: Cognitive Neuroscience's Measurement Problem Has a Solution

Cognitive neuroscience faces a measurement problem: core features of the human mind cannot be directly observed in the brain. For example, intentions are efficacious in behavior generation yet cannot be reduced to the sub‐personal quantities of neural activity without losing their purpose‐driven, normative character. This instrumental limitation is fundamental yet remains insufficiently recognized. To bring this issue to the forefront and reorient the field toward a solution, this brief commentary argues that theories of the mind–brain relation must meet the “Participation Criterion”: they must specify what measurable difference the presence of mental efficacy produces compared to its absence. When the Participation Criterion is accepted alongside the measurement problem, a feasible solution arises: the dynamical relevance of unobservable mental efficacy may manifest indirectly as increased unpredictability of observable brain activity, quantifiable via information‐theoretic entropy. The concept of “irruption” is introduced to specifically formalize this efficacy‐derived part of unexplained variability, thereby reframing context‐dependent “noise” in the brain as a key signature of the intentional mind at work. The theoretical proposal offers new avenues for research in cognitive science and clinical interventions.