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.

As this opinion may appear somewhat extraordinary, it may not be improper to confirm it by some other considerations.
A passion is an original existence, or, if you will, modification of existence, and contains not any representative quality, which renders it a copy of any other existence or modification.

When I am angry, I am actually possest with the passion, and in that emotion have no more a reference to any other object, than when I am thirsty, or sick, or more than five foot high.

It is impossible, therefore, that this passion can be opposed by, or be contradictory to truth and reason; since this contradiction consists in the disagreement of ideas, considered as copies, with those objects, which they represent.
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.