'Tacit consent' has long interested historians of political thought and political philosophers, but its nuances nevertheless remain unappreciated. It has its roots in the Roman law concept of a 'tacit declaration of will'. Explicating this concept allows a new conception of tacit consent to be proposed, which I term the 'tacit declaration of consent'. The tacit declaration of consent avoids both the triviality of common sense views and a weakness in Hobbes' account. Unlike other contemporary philosophical accounts, it avoids fictions and meets the condition of intentionality. Furthermore, it also advances understanding of the sorts of claim offered by proponents of a tacit consent-based theory of political obligation, whilst facilitating a more radical critique. The tacit consent-based theory of political obligation is not simply limited in application, but indefensible. It unwarrantedly transposes onto tacit consent the potentially fictional character of declarations of will.