On the Will by Baruch Spinoza

Now that we know the nature of Good and Evil, Truth and Falsity, and also wherein the well-being of a perfect man consists, it is time to begin to examine ourselves, and to see whether we attain to such well-being voluntarily or of necessity.

To this end it is necessary to inquire what the Will is, according to those who posit a Will and wherein it is different from Desire. Desire, we have said, is the inclination which the soul has towards something which it chooses as a good; whence it follows that before our desire inclines towards something outside, we have already inwardly decided that such a thing is good, and this affirmation, or, stated more generally, the power to affirm and to deny, is called the Will.