"The will is a principle agent and its affection of love is an instrument, since the will has it in [its] use and its power for the purpose of being expedited and efficacious (or intense) for an action to be performed. This is like a horse, having health throughout its body, that may use it [i.e. health] for running quickly. It would be an instrument of the horse with regard to velocity in a race. And affection is like this, that insofar as it is an instrument of the will, it is love. Love is a certain health of the will, but insofar as it stimulates by its healthy temperance for the intended motion, it has the nature of an inhabitant of the principle agent, and the will an instrument to the instrument. This is like a horse who runs quickly, having been furiously agitated. The fury itself is like an inhabitant of the horse and the horse itself is an instrument [of the fury]."