All contemporary frameworks of mental capacity stipulate that we must begin from the presumption that an adult has capacity. This presumption is crucial, as it manifests respect for autonomy and guards against prejudice and paternalism on the part of the evaluator. Given its ubiquity, we might presume that we all understand the presumption’s meaning and application in the same way. Evidence demonstrates that this is not the case and that this has led to harm in vulnerable persons. There is thus (...) strong reason to question our presumptions about the presumption of capacity. We distinguish between two main ways of understanding and applying the presumption of capacity, and advocate for the one that we argue mitigates risk of harm. Our proposed interpretation offers many advantages in that it is consonant with actual practice of capacity evaluations, precludes confused and abusive avoidance of needed evaluations, and preserves the respect for autonomy motivating the presumption in the first place. (shrink)