P5: The force and growth of any passion, and its perseverance in existing, are not defined by the power by which we strive to persevere in existing, but by the power of an external cause compared with our own.

Dem.: The essence of a passion cannot be explained through our essence alone (by IIID1 and D2), i.e. (by IIIP7), the power of a passion cannot be defined by the power by which we strive to persevere in our being; but (as has been shown in IIP16) it must necessarily be defined by the power of an external cause compared with our own, q.e.d.