 Tho’ the several resembling instances, which give rise to the idea of power, have no influence on each other, and can never produce any new quality in the object, which can be a model of that idea [of power or causation], yet the observation of this resemblance produces a new impression in the mind, which is its real model…. Necessity, then, is the effect of this observation, and is nothing but an internal impression of the mind, or a determination to carry our thoughts from one object to another. (1739–40: I.III.14, para. 20)