The case is the same as in colours.

A particular shade of any colour may acquire a new degree of liveliness or brightness without any other variation.

But when you produce any other variation, it is no longer the same shade or colour.

So that as belief does nothing but vary the manner, in which we conceive any object, it can only bestow on our ideas an additional force and vivacity.

An opinion, therefore, or belief may be most accurately defined, a lively idea related to or associated with a present impression.
We may here take occasion to observe a very remarkable error, which being frequently inculcated in the schools, has become a kind of establishd maxim, and is universally received by all logicians.