What may at first occur on this head, is, that as nothing can be contrary to truth or reason, except what has a reference to it, and as the judgments of our understanding only have this reference, it must follow, that passions can be contrary to reason only so far as they are accompanyed with some judgment or opinion.  According to this principle, which is so obvious and natural, it is only in two senses, that any affection can be called unreasonable.  First, When a passion, such as hope or fear, grief or joy, despair or security, is founded on the supposition or the existence of objects, which really do not exist.  Secondly, When in exerting any passion in action, we chuse means insufficient for the designed end, and deceive ourselves in our judgment of causes and effects.  Where a passion is neither founded on false suppositions, nor chuses means insufficient for the end, the understanding can neither justify nor condemn it.  It is not contrary to reason to prefer the destruction of the whole world to the scratching of my finger.  It is not contrary to reason for me to chuse my total ruin, to prevent the least uneasiness of an Indian or person wholly unknown to me.  It is as little contrary to reason to prefer even my own acknowledgeed lesser good to my greater, and have a more ardent affection for the former than the latter.  A trivial good may, from certain circumstances, produce a desire superior to what arises from the greatest and most valuable enjoyment; nor is there any thing more extraordinary in this, than in mechanics to see one pound weight raise up a hundred by the advantage of its situation.  In short, a passion must be accompanyed with some false judgment. in order to its being unreasonable; and even then it is not the passion, properly speaking, which is unreasonable, but the judgment.

The consequences are evident.  Since a passion can never, in any sense, be called unreasonable, but when founded on a false supposition. or when it chuses means insufficient for the designed end, it is impossible, that reason and passion can ever oppose each other, or dispute for the government of the will and actions.  The moment we perceive the falshood of any supposition, or the insufficiency of any means our passions yield to our reason without any opposition.  I may desire any fruit as of an excellent relish; but whenever you convince me of my mistake, my longing ceases.  I may will the performance of certain actions as means of obtaining any desired good; but as my willing of these actions is only secondary, and founded on the supposition, that they are causes of the proposed effect; as soon as I discover the falshood of that supposition, they must become indifferent to me.