Reason is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them. - David Hume

Reason is, and ought only to be the slave of the passions.

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 accompany'd with some judgment or opinion. According to this principle, which is so obvious and natural, `tis only in two senses, that any affection can be call'd 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 design'd 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. `Tis not contrary to reason to prefer the destruction of the whole world to the scratching of my finger. `Tis 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. `Tis as little contrary to reason to prefer even my own acknowledge'd 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 accompany'd with some false judgment. in order to its being unreasonable; and even then `tis not the passion, properly speaking, which is unreasonable, but the judgment.

In a word, human life is more governed by fortune than by reason; is to be regarded more as a dull pastime than as a serious occupation; and is more influenced by particular humour, than by general principles. Shall we engage ourselves in it with passion and anxiety? It is not worthy of so much concern. Shall we be indifferent about what happens? We lose all the pleasure of the game by our phlegm and carelessness. While we are reasoning concerning life, life is gone; and death, though perhaps they receive him differently, yet treats alike the fool and the philosopher.

[T]he Old Testament, [...] if considered as a general rule of conduct, would lead to consequences destructive of all principles of humanity and morality.