It isn’t difficult to provide other examples of the same phenomenon; the present subject of metaphysics supplies them in abundance. An argument that would have been found convincing in a reasoning about history or politics has little or no influence in abstruser subjects such as metaphysics, even when it is perfectly understood; and that is because understanding it requires a study and an effort of thought, which disturbs the operation of our sentiments on which the belief depends. The case is the same in other subjects. The straining of the imagination always hinders the regular flowing of the passions and sentiments. A tragic poet who represented his heroes as talking cleverly and inventively in their misfortunes would never touch the passions. Just as the •emotions of the soul prevent any •subtle reasoning and reflection, so •reflective thinking tends to quell •emotions. The mind, as well as the body, seems to be endowed with a certain definite amount of force and activity which it employs in one action only at the expense of all the rest. This is more evidently true where the actions are of quite different kinds; for then the force of the mind is not only redirected but its disposition is changed, making us incapable of a sudden switch from one action to the other, let alone of performing both at once. No wonder, then, that the belief arising from a subtle reasoning lessens in proportion to the efforts that the imagination makes to enter into the reasoning and to conceive it in all its parts. Belief, being a lively conception, can never be complete when it is not founded on something natural and easy.
Tnh 1 4 01 11