For after we have observed the resemblance in a sufficient number of instances, we immediately feel a determination of the mind to pass from one object to its usual attendant, and to conceive it in a stronger light upon account of that relation.

This determination is the only effect of the resemblance; and therefore must be the same with power or efficacy, whose idea is derived from the resemblance.

The several instances of resembling conjunctions lead us into the notion of power and necessity.

These instances are in themselves totally distinct from each other, and have no union but in the mind, which observes them, and collects their ideas.

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.
Without considering it in this view, we can never arrive at the most distant notion of it, or be able to attribute it either to external or internal objects, to spirit or body, to causes or effects.
The necessary connexion betwixt causes and effects is the foundation of our inference from one to the other.