What is commonly, in a popular sense, called reason, and is so much recommended in moral discourses, is nothing but a general and a calm passion, which takes a comprehensive and distant view of its object, and actuates the will, without exciting any sensible emotion. A man, we say, is diligent in his profession from reason; that is, from a calm desire of riches and a fortune. A man adheres to justice from reason; that is, from a calm regard to a character with himself and others.
Hume, A Dissertation on the Passions, Section V. This is very important for understanding Hume's view that reason only serves the passions: part of what makes the view plausible on his account is that much that other people attribute to reason he attributes to the passions: calm passions are a sort of emotional fixing on a general view of the situation, rather than simply a knee-jerk reaction, and thus influence action by a steady and constant pressure.
