a degree of belief, which is sufficient for our purpose, either in philosophy or common life?_ I answer, that after the first and second decision, as the action of the mind becomes forced and unnatural, and the ideas faint and obscure, though the principles of judgment, and the balancing of opposite causes be the same as at the very beginning, yet their influence on the imagination, and the vigour they add to, or diminish from, the thought, is by no means equal. Where the mind reaches not its objects with easiness and facility, the same principles have not the same effect as in a more natural conception of the ideas; nor does the imagination feel a sensation, which holds any proportion with that which arises from its common judgments and opinions. The attention is on the stretch; the posture of the mind is uneasy; and the spirits being diverted from their natural course, are not governed in their movements by the same laws, at least not to the same degree, as when they flow in their usual channel. If we desire similar instances, 'twill not be very difficult to find them. The present subject of metaphysics will supply us abundantly. The same argument, which would have been esteemed convincing in a reasoning concerning history or politics, has little or no influence in these abstruser subjects, even though it be perfectly comprehended; and that because there is required a study and an effort of thought, in order to its being comprehended: and this effort of thought 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, that would represent his heroes as very ingenious and witty in their misfortunes, would never touch the passions. As the emotions of the soul prevent any subtile reasoning and reflection, so these latter actions of the mind are equally prejudicial to the former. The mind, as well as the body, seems to be endowed with a certain precise degree of force and activity, which it never employs in one action, but at the expense of all the rest. This is more evidently true, where the actions are of quite different natures; since in that case the force of the mind is not only diverted, but even the disposition changed, so as to render us incapable of a sudden transition from one action to the other, and still more of performing both at once. No wonder, then, the conviction, which arises from a subtile reasoning, diminishes in proportion to the efforts which the imagination makes to enter into the reasoning, and to conceive it in all its parts. Belief, being a lively conception, can never be entire, where it is not founded on something natural and easy.