Thomas Aquinas

“ For every power extends to those things in which may be considered the aspect of the object of that power in any way whatever: thus the sight extends to all things whatsoever that are in any way colored. Now the aspect of good, which is the object of the power of the will, may be found not only in the end, but also in the means.
If, however, we speak of the will in regard to its act, then, properly speaking, volition is of the end only. Because every act denominated from a power, designates the simple act of that power: thus "to understand" designates the simple act of the understanding. ”

“ I answer that, The will is a rational appetite. Now every appetite is only of something good. The reason of this is that the appetite is nothing else than an inclination of a person desirous of a thing towards that thing. Now every inclination is to something like and suitable to the thing inclined. Since, therefore, everything, inasmuch as it is being and substance, is a good, it must needs be that every inclination is to something good. ”

“ Hence it is evident that the will is moved by one and the same movement, to the end, as the reason for willing the means; and to the means themselves. But it is another act whereby the will is moved to the end absolutely. And sometimes this act precedes the other in time; for example when a man first wills to have health, and afterwards deliberating by what means to be healed, wills to send for the doctor to heal him. The same happens in regard to the intellect: for at first a man understands the principles in themselves ”