The foundation of our inference is the transition arising from the accustomed union.

These are, therefore, the same.
The idea of necessity arises from some impression.

There is no impression conveyed by our senses, which can give rise to that idea.

It must, therefore, be derived from some internal impression, or impression of reflection.

There is no internal impression, which has any relation to the present business, but that propensity, which custom produces, to pass from an object to the idea of its usual attendant.