Note 2 The Idea Of Necessary Connexion
from An Enquiry Concerning Human Understanding

It may be pretended, that the resistance which we meet with in bodies, obliging us frequently to exert our force, and call up all our power, this gives us the idea of force and power. It is this nisus or strong endeavour, of which we are conscious that is the original impression from which this idea is copied. But, first, we attribute power to a vast number of objects, where we never can suppose this resistance of exertion of force to take place, to the Supreme Being, who never meets with any resistance to the mind in its command over its ideas and limbs, in common thinking and motion, where the effect follows immediately upon the will, without any exertion or summoning up of force; to inanimate matter, which is not capable of this sentiment. Secondly, This sentiment of an endeavour to overcome resistance has no known connexion with any event: What follows it, we know by experience; but could not know it a priori. It must, however, be confessed, that the animal nisus, which we experience, though it can afford no accurate precise idea of power, enters very much into that vulgar, inaccurate idea, which is formed of it.