If this answer satisfies not, it is plain the meaning of the question, What determines the will?
is this,--What moves the mind, in every particular instance, to determine its general power of directing, to this or that particular motion or rest?
And to this I answer,--The motive for continuing in the same state or action, is only the present satisfaction in it; the motive to change is always some uneasiness: nothing setting us upon the change of state, or upon any new action, but some uneasiness.

This is the great motive that works on the mind to put it upon action, which for shortness' sake we will call determining of the will, which I shall more at large explain.
30.

Will and Desire must not be confounded.
But, in the way to it, it will be necessary to premise, that, though I have above endeavoured to express the act of volition, by CHOOSING, PREFERRING, and the like terms, that signify desire as well as volition, for want of other words to mark that act of the mind whose proper name is WILLING or VOLITION; yet, it being a very simple act, whosoever desires to understand what it is, will better find it by reflecting on his own mind, and observing what it does when it wills, than by any variety of articulate sounds whatsoever.

This caution of being careful not to be misled by expressions that do not enough keep up the difference between the WILL and several acts of the mind that are quite distinct from it, I think the more necessary, because I find the will often confounded with several of the affections, especially DESIRE, and one put for the other; and that by men who would not willingly be thought not to have had very distinct notions of things, and not to have writ very clearly about them.

This, I imagine, has been no small occasion of obscurity and mistake in this matter; and therefore is, as much as may be, to be avoided.